Knowledge (XXG)

Triangle

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2453: 1903: 3158: 1022: 2525: 2448:{\displaystyle {\begin{aligned}T&={\tfrac {1}{2}}{\begin{vmatrix}x_{A}&x_{B}&x_{C}\\y_{A}&y_{B}&y_{C}\\1&1&1\end{vmatrix}}={\tfrac {1}{2}}{\begin{vmatrix}x_{A}&x_{B}\\y_{A}&y_{B}\end{vmatrix}}+{\tfrac {1}{2}}{\begin{vmatrix}x_{B}&x_{C}\\y_{B}&y_{C}\end{vmatrix}}+{\tfrac {1}{2}}{\begin{vmatrix}x_{C}&x_{A}\\y_{C}&y_{A}\end{vmatrix}}\\&={\tfrac {1}{2}}(x_{A}y_{B}-x_{B}y_{A}+x_{B}y_{C}-x_{C}y_{B}+x_{C}y_{A}-x_{A}y_{C}),\end{aligned}}} 3798: 1687: 526: 329: 2575: 343: 448: 49: 1118: 3139: 3959: 3950: 3718: 696: 357: 535: 399: 632: 623: 385: 371: 1299: 3727: 3149: 3627: 2893: 675:: the object can be balanced on its centroid in a uniform gravitational field. The centroid cuts every median in the ratio 2:1, i.e. the distance between a vertex and the centroid is twice the distance between the centroid and the midpoint of the opposite side. If one reflects a median in the angle bisector that passes through the same vertex, one obtains a 2509:
states that the sum of the lengths of any two sides of a triangle must be greater than or equal to the length of the third side. A triangle with three given positive side lengths exists if and only if those side lengths satisfy the triangle inequality. The sum of two side lengths can equal the length
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from pressure to one of its points, triangles are sturdy because specifying the lengths of all three sides determines the angles. Therefore, a triangle will not change shape unless its sides are bent or extended or broken or if its joints break; in essence, each of the three sides supports the other
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This diagram illustrates the geometric principle of angle-angle-side triangle congruence: given triangle ABC and triangle A'B'C', triangle ABC is congruent with triangle A'B'C' if and only if: angle CAB is congruent with angle C'A'B', and angle ABC is congruent with angle A'B'C', and BC is congruent
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The triangles in both spaces have properties different from the triangles in Euclidean space. For example, as mentioned above, the internal angles of a triangle in Euclidean space always add up to 180°. However, the sum of the internal angles of a hyperbolic triangle is less than 180°, and for any
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have exactly the same size and shape. All pairs of congruent triangles are also similar, but not all pairs of similar triangles are congruent. Given two congruent triangles, all pairs of corresponding interior angles are equal in measure, and all pairs of corresponding sides have the same length.
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Each triangle has many special points inside it, on its edges, or otherwise associated with it. They are constructed by finding three lines associated symmetrically with the three sides (or vertices) and then proving that the three lines meet in a single point. An important tool for proving the
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Every acute triangle has three inscribed squares (squares in its interior such that all four of a square's vertices lie on a side of the triangle, so two of them lie on the same side and hence one side of the square coincides with part of a side of the triangle). In a right triangle two of the
614:(red line). The center of the nine-point circle lies at the midpoint between the orthocenter and the circumcenter, and the distance between the centroid and the circumcenter is half that between the centroid and the orthocenter. Generally, the incircle's center is not located on Euler's line. 493:
implies that if the circumcenter is located on the side of the triangle, then the angle opposite that side is a right angle. If the circumcenter is located inside the triangle, then the triangle is acute; if the circumcenter is located outside the triangle, then the triangle is obtuse.
3134:{\displaystyle {\frac {{\overline {PA}}\cdot {\overline {QA}}}{{\overline {CA}}\cdot {\overline {AB}}}}+{\frac {{\overline {PB}}\cdot {\overline {QB}}}{{\overline {AB}}\cdot {\overline {BC}}}}+{\frac {{\overline {PC}}\cdot {\overline {QC}}}{{\overline {BC}}\cdot {\overline {CA}}}}=1.} 280:
A triangle is a figure consisting of three line segments, each of whose endpoints are connected. This forms a polygon with three sides and three angles. The terminology for categorizing triangles is more than two thousand years old, having been defined in Book One of Euclid's
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inscribed squares. An obtuse triangle has only one inscribed square, with a side coinciding with part of the triangle's longest side. Within a given triangle, a longer common side is associated with a smaller inscribed square. If an inscribed square has a side of length
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Two systems avoid that feature, so that the coordinates of a point are not affected by moving the triangle, rotating it, or reflecting it as in a mirror, any of which gives a congruent triangle, or even by rescaling it to a similar triangle:
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As mentioned above, every triangle has a unique circumcircle, a circle passing through all three vertices, whose center is the intersection of the perpendicular bisectors of the triangle's sides. Furthermore, every triangle has a unique
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The definition by Euclid states that an isosceles triangle is a triangle with exactly two equal sides. By the modern definition, it has at least two equal sides, implying that an equilateral triangle is a special case of isosceles
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If and only if one pair of corresponding sides of two triangles are in the same proportion as another pair of corresponding sides, and their included angles have the same measure, then the triangles are similar. (The
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of that point. If the interior point is the circumcenter of the reference triangle, the vertices of the pedal triangle are the midpoints of the reference triangle's sides, and so the pedal triangle is called the
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Advances in Discrete and Computational Geometry: Proceedings of the 1996 AMS-IMS-SIAM Joint Summer Research Conference, Discrete and Computational Geometry—Ten Years Later, July 14-18, 1996, Mount Holyoke
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spherical triangle, the sum is more than 180°. In particular, it is possible to draw a triangle on a sphere such that the measure of each of its internal angles equals 90°, adding up to a total of 270°. By
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Any three angles that add to 180° can be the internal angles of a triangle. Infinitely many triangles have the same angles, since specifying the angles of a triangle does not determine its size. (A
2687:, and to use Cartesian coordinates. While convenient for many purposes, this approach has the disadvantage of all points' coordinate values being dependent on the arbitrary placement in the plane. 1908: 889: 1475: 729:. The sum of the measures of the three exterior angles (one for each vertex) of any triangle is 360 degrees, and indeed, this is true for any convex polygon, no matter how many sides it has. 1682: 2589:, a polygon is subdivided into multiple triangles that are attached edge-to-edge, with the property that their vertices coincide with the set of vertices of the polygon. In the case of a 4061: 1098:
AAS: Two angles and a corresponding (non-included) side in a triangle have the same measure and length, respectively, as those in the other triangle. (This is sometimes referred to as
1600: 2792: 1243: 1153:, which has area 1. There are several ways to calculate the area of an arbitrary triangle. One of the oldest and simplest is to take half the product of the length of one side 3760:, which passes through the triangle's vertices and has its center at the triangle's centroid. Of all ellipses going through the triangle's vertices, it has the smallest area. 1420: 725:) to an interior angle. The measure of an exterior angle of a triangle is equal to the sum of the measures of the two interior angles that are not adjacent to it; this is the 2794:
specify the point's location by the relative weights that would have to be put on the three vertices in order to balance the otherwise weightless triangle on the given point.
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As discussed above, every triangle has a unique inscribed circle (incircle) that is interior to the triangle and tangent to all three sides. Every triangle has a unique
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It is well known that the incenter of a Euclidean triangle lies on its Euler line connecting the centroid and the circumcenter if and only if the triangle is isosceles.
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ASA: Two interior angles and the side between them in a triangle have the same measure and length, respectively, as those in the other triangle. (This is the basis of
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one pair of internal angles of two triangles have the same measure as each other, and another pair also have the same measure as each other, the triangles are similar.
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Triangles are classified into different types based on their angles and the lengths of their sides. Relations between angles and side lengths are a major focus of
2848: 2754: 2665: 2639: 608:. The orthocenter (blue point), the center of the nine-point circle (red), the centroid (orange), and the circumcenter (green) all lie on a single line, known as 3698: 744:. In a scalene triangle, the trigonometric functions can be used to find the unknown measure of either a side or an internal angle; methods for doing so use the 4090:
relating the properties of a triangle in the space to properties of a corresponding triangle in a model space like hyperbolic or elliptic space. For example, a
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of a triangle is the ellipse inscribed within the triangle tangent to its sides at the contact points of its excircles. For any ellipse inscribed in a triangle
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can be defined without reference to a notion of distance or squares. In any affine space (including Euclidean planes), every triangle with the same base and
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subset of the plane lying between three mutually tangent convex regions. These sides are three smoothed curved lines connecting their endpoints called the
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This formula can be proven by cutting up the triangle and an identical copy into pieces and rearranging the pieces into the shape of a rectangle of base
823:, each of them between 0° and 180°, to be the angles of a triangle can also be stated using trigonometric functions. For example, a triangle with angles 511:
of the altitude. The length of the altitude is the distance between the base and the vertex. The three altitudes intersect in a single point, called the
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of a triangle is a straight line through a vertex that cuts the corresponding angle in half. The three angle bisectors intersect in a single point, the
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or medial triangle. The midpoint triangle subdivides the reference triangle into four congruent triangles which are similar to the reference triangle.
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with vertices given by the six intersections of the sides of a triangle with the three lines that are parallel to the sides and that pass through its
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of the side and being perpendicular to it, forming a right angle with it. The three perpendicular bisectors meet in a single point, the triangle's
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Algorithmic Foundation of Robotics VII: Selected Contributions of the Seventh International Workshop on the Algorithmic Foundations of Robotics
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SAS Postulate: Two sides in a triangle have the same length as two sides in the other triangle, and the included angles have the same measure.
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One way to identify locations of points in (or outside) a triangle is to place the triangle in an arbitrary location and orientation in the
763:, has internal angles of 0° and 180°; whether such a shape counts as a triangle is a matter of convention.) The conditions for three angles 5534: 550:
is a straight line through the orthocenter (blue), the center of the nine-point circle (red), centroid (orange), and circumcenter (green).
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of a reference triangle has its vertices at the points of tangency of the reference triangle's excircles with its sides (not extended).
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edges. The edges of a circular triangle may be either convex (bending outward) or concave (bending inward). The intersection of three
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The area formula for a triangle can be proven by cutting two copies of the triangle into pieces and rearranging them into a rectangle.
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of the opposite side, and divides the triangle into two equal areas. The three medians intersect in a single point, the triangle's
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Triangles have many types based on the length of the sides and on the angles. A triangle whose sides are all the same length is an
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of a reference triangle has its vertices at the three points of tangency of the reference triangle's sides with its incircle. The
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If and only if three pairs of corresponding sides of two triangles are all in the same proportion, then the triangles are similar.
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Pocchiola, Michel; Vegter, Gert (1999). "On Polygonal Covers". In Chazelle, Bernard; Goodman, Jacob E.; Pollack, Richard (eds.).
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Oxman, Victor; Stupel, Moshe (2013). "Why Are the Side Lengths of the Squares Inscribed in a Triangle so Close to Each Other?".
3778:, one with maximal area can be found in linear time; its vertices may be chosen as three of the vertices of the given polygon. 436:. Similarly, lines associated with a triangle are often constructed by proving that three symmetrically constructed points are 287:. The names used for modern classification are either a direct transliteration of Euclid's Greek or their Latin translations. 594:. The remaining three points for which it is named are the midpoints of the portion of altitude between the vertices and the 3588:. The smallest possible ratio of the side of one inscribed square to the side of another in the same non-obtuse triangle is 671:
or geometric barycenter. The centroid of a rigid triangular object (cut out of a thin sheet of uniform density) is also its
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gives a useful general criterion. In this section, just a few of the most commonly encountered constructions are explained.
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with the same base whose opposite side lies on the parallel line. This affine approach was developed in Book 1 of Euclid's
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of a triangle is a straight line through a vertex and perpendicular to the opposite side. This opposite side is called the
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The measures of the interior angles of the triangle always add up to 180 degrees (same color to point out they are equal).
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Eddy, R. H.; Fritsch, R. (1994). "The Conics of Ludwig Kiepert: A Comprehensive Lesson in the Geometry of the Triangle".
5662: 3822: 715:. This allows the determination of the measure of the third angle of any triangle, given the measure of two angles. An 455:
is the center of a circle passing through the three vertices of the triangle; the intersection of the altitudes is the
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forms a circular triangle whose sides are all convex. An example of a circular triangle with three convex edges is a
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The largest possible ratio of the area of the inscribed square to the area of the triangle is 1/2, which occurs when
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From an interior point in a reference triangle, the nearest points on the three sides serve as the vertices of the
588:. The midpoints of the three sides and the feet of the three altitudes all lie on a single circle, the triangle's 2730:
indicate that the ratio of the distance of the point from the first side to its distance from the second side is
1089: 574:. The incircle is the circle that lies inside the triangle and touches all three sides. Its radius is called the 328: 31: 6611: 6156: 4852: 4018: 2582: 756: 1549: 2671:, a vertex connected by two other vertices, the diagonal between which lies entirely within the polygon. The 342: 6536: 5961: 2765: 1007:{\displaystyle \cos ^{2}\alpha +\cos ^{2}\beta +\cos ^{2}\gamma +2\cos(\alpha )\cos(\beta )\cos(\gamma )=1.} 265: 5447:
Allaire, Patricia R.; Zhou, Junmin; Yao, Haishen (2012). "Proving a nineteenth century ellipse identity"".
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has its apex (the third vertex) on a line parallel to the base, and their common area is half of that of a
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sides. This article is about straight-sided triangles in Euclidean geometry, except where otherwise noted.
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if, given any two points in that subset, the whole line segment joining them also lies within that subset.
4106: 3840:. Any pseudotriangle can be partitioned into many pseudotriangles with the boundaries of convex disks and 3833: 1021: 733: 726: 207: 6962: 6902: 6541: 6365:
Verdiyan, Vardan; Salas, Daniel Campos (2007). "Simple trigonometric substitutions with broad results".
3736: 3157: 2695: 2586: 2569: 1741: 1714: 1070: 1036: 600:. The radius of the nine-point circle is half that of the circumcircle. It touches the incircle (at the 356: 227: 5686:
Chandran, Sharat; Mount, David M. (1992). "A parallel algorithm for enclosed and enclosing triangles".
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of the altitude, and the point where the altitude intersects the base (or its extension) is called the
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Longuet-Higgins, Michael S. (2003). "On the ratio of the inradius to the circumradius of a triangle".
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Edmonds, Allan L.; Hajja, Mowaffaq; Martini, Horst (2008). "Orthocentric simplices and biregularity".
3983:, roughly speaking a flat space. This means triangles may also be discovered in several spaces, as in 3797: 2537:
two. A rectangle, in contrast, is more dependent on the strength of its joints in a structural sense.
1384: 398: 6846: 6616: 6546: 6488: 6256: 6063: 5567: 5546: 5526: 5449: 441: 334: 291: 283: 3591: 2820:. This ellipse has the greatest area of any ellipse tangent to all three sides of the triangle. The 6952: 6927: 6897: 6892: 6851: 6566: 6187: 5921: 5838: 4838: 4012: 3992: 3967: 3935: 3745: 3203:
squares coincide and have a vertex at the triangle's right angle, so a right triangle has only two
2813: 2519: 2506: 2500: 1849: 1799: 1749: 1706: 1686: 1483: 722: 585: 499: 384: 370: 219: 4265: 3650:, the Lemoine hexagon is interior to the triangle with two vertices on each side of the triangle. 6983: 6957: 6498: 6173: 6103: 5957:
Mathematical Techniques: An Introduction for the Engineering, Physical, and Mathematical Sciences
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SSS: Each side of a triangle has the same length as the corresponding side of the other triangle.
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of the triangle. The orthocenter lies inside the triangle if and only if the triangle is acute.
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of a reference triangle (other than a right triangle) is the triangle whose sides are on the
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Berg, Mark Theodoor de; Kreveld, Marc van; Overmars, Mark H.; Schwarzkopf, Otfried (2000).
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of the third side only in the case of a degenerate triangle, one with collinear vertices.
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Hungerbühler, Norbert (1994). "A short elementary proof of the Mohr-Mascheroni theorem".
3825:. Alternatively, it can be constructed by rounding the sides of an equilateral triangle. 2827: 2733: 2644: 2618: 2585:
means the partition of any planar object into a collection of triangles. For example, in
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that passes through the triangle's three vertices, its centroid, and its circumcenter.
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for the vertices of a triangle, its relative oriented area can be calculated using the
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This is a total of six equalities, but three are often sufficient to prove congruence.
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Bailey, Herbert; Detemple, Duane (1998). "Squares inscribed in angles and triangles".
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states that every simple polygon that is not itself a triangle has at least two ears.
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Silvester, John R. (March 2017). "Extremal area ellipses of a convex quadrilateral".
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Another relation between the internal angles and triangles creates a new concept of
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is a line (dashed green) parallel to the base. This is the Euclidean version of
1486:, is a formula for finding the area of a triangle from the lengths of its sides 1298: 631: 622: 596: 513: 456: 303: 200: 5852: 6861: 6717: 6707: 6591: 6347: 6231: 6136: 6076: 6043: 6031: 5887: 5699: 5606: 5479: 5462: 5163: 5150:
Smith, Geoff; Leversha, Gerry (November 2007). "Euler and triangle geometry".
5056: 4598: 4154: 3995:, and it can be obtained by drawing on a negatively curved surface, such as a 3726: 3626: 2698:
specify the relative distances of a point from the sides, so that coordinates
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Because the ratios between areas of shapes in the same plane are preserved by
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for any two sides of a polygon is the internal angle between those two sides.)
1027: 5842: 5064: 4003:, and it can be obtained by drawing on a positively curved surface such as a 2812:
which is interior to the triangle and tangent at the midpoints of the sides.
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The incircle of a triangle, and the intersection of the medians known as the
6836: 6826: 6803: 6793: 6783: 6712: 6621: 6586: 5777: 3841: 3148: 677: 469: 437: 314:, and a triangle in which one of it angles is greater than that angle is an 118: 6338:. In Akella, Srinivas; Amato, Nancy M.; Huang, Wesley; Mishra, Bud (eds.). 5372:"LAS 100 — Freshman Seminar — Fall 1996: Reasoning with shape and quantity" 6154:
Oldknow, Adrian (1995). "Computer Aided Research into Triangle Geometry".
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demonstrates a symmetry where six points lie on the edge of the triangle.
183:, any two points determine a unique line segment situated within a unique 17: 6841: 6831: 6788: 6747: 6676: 6666: 667: 662: 641: 605: 580: 570: 564: 474: 460: 232: 108: 5171: 4559:
Geometry Turned On: Dynamic Software in Learning, Teaching, and Research
3471:{\displaystyle q_{a}={\frac {2Ta}{a^{2}+2T}}={\frac {ah_{a}}{a+h_{a}}}.} 6798: 6778: 6691: 6686: 6681: 6671: 6646: 6601: 6462: 6177: 6107: 5938: 5198: 4102: 3647: 3639: 2817: 2667:
diagonals. Triangulation of a simple polygon has a relationship to the
2545: 1044: 310:, a triangle in which all of its angles are less than that angle is an 100: 3623:. Both of these extreme cases occur for the isosceles right triangle. 6606: 6009:
Geometry Transformed: Euclidean Plane Geometry Based on Rigid Motions
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This article is about the basic geometric shape. For other uses, see
6169: 6099: 5930: 432:, which gives a criterion for determining when three such lines are 230:
enclosed by three sides which are straight relative to the surface (
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are known, then the altitude can be calculated using trigonometry,
6651: 6431: 6428:. Lists some 5200 interesting points associated with any triangle. 5820:
Structure and Form in Design: Critical Ideas for Creative Practice
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International Journal of Computational Geometry & Applications
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Triangles are strong in terms of rigidity, but while packed in a
6125:"On Geodesic Triangles with Right Angles in a Dually Flat Space" 1126: 80: 6435: 5574:. DMV Seminar 25. Basel: Birkhäuser Verlag. pp. viii+112. 4083:
is the fraction of the sphere's area enclosed by the triangle.
3255:, part of which side coincides with a side of the square, then 473:
of a side of a triangle is a straight line passing through the
459:. The intersection of the angle bisectors is the center of the 4940: 2552:). Tessellated triangles still maintain superior strength for 2548:
under compression (hence the prevalence of hexagonal forms in
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A special case of concave circular triangle can be seen in a
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Circular triangles with a mixture of convex and concave edges
740:, as well as the other functions. They can be defined as the 6317:
The Classification of Quadrilaterals: A Study in Definition
5628:(2 ed.). Berlin Heidelberg: Springer. pp. 45–61. 3548:, and the altitude of the triangle from the base of length 721:
of a triangle is an angle that is a linear pair (and hence
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is always 180 degrees. This fact is equivalent to Euclid's
5847:. Vol. 1 (2nd ed.). Cambridge University Press. 3752:
to the reference triangle's circumcircle at its vertices.
191:
determine a unique triangle situated within a unique flat
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Progress in Information Geometry: Theory and Applications
4562:. The Mathematical Association of America. pp. 3–4. 3999:. Likewise, a triangle in spherical geometry is called a 294:, a triangle with two sides having the same length is an 3677:
can be inscribed in a triangle of area at most equal to
705:
sum of the measures of the interior angles of a triangle
681:. The three symmedians intersect in a single point, the 298:, and a triangle with three different-length sides is a 3735:
The circumscribed circle tangent to a triangle and the
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equals one-half the product of height and base length.
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Problems in Euclidean Space: Applications of Convexity
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is defined by comparison with a square of side length
5730:. Vol. 19. Mathematical Association of America. 5276: 4144:
Again, in all cases "mirror images" are also similar.
4069: 4021: 4015:, the sum of the angles of a triangle on a sphere is 3899: 3870: 3850: 3683: 3663: 3594: 3574: 3554: 3520: 3484: 3375: 3355: 3335: 3308: 3288: 3261: 3241: 3214: 2896: 2876: 2856: 2830: 2768: 2736: 2704: 2647: 2621: 2600: 2463: 1906: 1852: 1802: 1752: 1612: 1552: 1532: 1512: 1492: 1430: 1387: 1365: 1343: 1319: 1279: 1255: 1207: 1185: 1161: 1137: 892: 869: 849: 829: 809: 789: 769: 417:
Points, lines, and circles associated with a triangle
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with three corners and three sides, one of the basic
5346:"The area of a spherical triangle. Girard's Theorem" 5308: 5080:"Reflection-Induced Perspectivities Among Triangles" 3979:
A non-planar triangle is a triangle not included in
166:; the shortest segment between base and apex is the 138:, each one bounded by a pair of adjacent edges; the 6870: 6816: 6756: 6700: 6639: 6630: 6522: 6474: 6334:Vahedi, Mostafa; van der Stappen, A. Frank (2008). 5626:
Computational geometry: algorithms and applications
4535: 4533: 79: 69: 55: 41: 6131:. Signals and Communication Technology. Springer. 4075: 4055: 3914: 3885: 3856: 3692: 3669: 3615: 3580: 3560: 3540: 3506: 3470: 3361: 3341: 3321: 3294: 3274: 3247: 3227: 3133: 2882: 2862: 2842: 2786: 2748: 2722: 2659: 2633: 2606: 2479: 2447: 1884: 1834: 1784: 1676: 1594: 1538: 1518: 1498: 1469: 1414: 1371: 1349: 1325: 1285: 1261: 1237: 1191: 1167: 1143: 1006: 875: 855: 835: 815: 795: 775: 160:, in which case the opposite vertex is called the 154:. Sometimes an arbitrary edge is chosen to be the 2556:, however, which is why engineering makes use of 489:, the circle passing through all three vertices. 1470:{\displaystyle T={\tfrac {1}{2}}ab\sin \gamma .} 1030:are used here to show angle and side equalities. 5292: 5026: 4746: 4678: 3864:disks in a pseudotriangle, the partition gives 3844:, a process known as pseudo-triangulation. For 742:ratio between any two sides of a right triangle 578:. There are three other important circles, the 6084:Meisters, G. H. (1975). "Polygons have ears". 5745:Devadoss, Satyan L.; O'Rourke, Joseph (2011). 5106: 5014: 4305: 146:(180 degrees or π radians). The triangle is a 6447: 5668:The First Six Books of the Elements of Euclid 5416:Frame, Michael; Urry, Amelia (21 June 2016). 5238: 4741: 3991:. A triangle in hyperbolic space is called a 1677:{\displaystyle T={\sqrt {s(s-a)(s-b)(s-c)}}.} 1081:for a pair of triangles to be congruent are: 302:. A triangle in which one of the angles is a 124:while the sides connecting them, also called 8: 6336:"Caging Polygons with Two and Three Fingers" 6222:Ramsay, Arlan; Richtmyer, Robert D. (1995). 5262: 5041:"Twenty-one points on the nine-point circle" 4556:Schattschneider, Doris; King, James (1997). 4426: 2532:Unlike a rectangle, which may collapse into 1177:(the base) times the corresponding altitude 214:) also determine a triangle, for instance a 5572:Lectures on spaces of nonpositive curvature 5125: 5111: 4912: 3630:The Lemoine hexagon inscribed in a triangle 2544:arrangement triangles are not as strong as 1302:Applying trigonometry to find the altitude 655:of a triangle is a straight line through a 6636: 6454: 6440: 6432: 5419:Fractal Worlds: Grown, Built, and Imagined 5078:Moses, Peter; Kimberling, Charles (2009). 4461: 4410: 4394: 4323: 4234: 4207: 4176: 3700:. Equality holds only if the polygon is a 736:. The primary trigonometric functions are 318:. These definitions date back at least to 5981:"An Elementary Proof of Marden's Theorem" 5920: 5137: 4068: 4056:{\displaystyle 180^{\circ }\times (1+4f)} 4026: 4020: 3898: 3869: 3849: 3682: 3662: 3648:simple form or its self-intersecting form 3605: 3598: 3593: 3573: 3553: 3530: 3519: 3489: 3483: 3456: 3438: 3428: 3407: 3389: 3380: 3374: 3354: 3334: 3313: 3307: 3287: 3266: 3260: 3240: 3219: 3213: 3107: 3089: 3072: 3054: 3051: 3030: 3012: 2995: 2977: 2974: 2953: 2935: 2918: 2900: 2897: 2895: 2875: 2855: 2829: 2767: 2735: 2703: 2646: 2620: 2599: 2472: 2464: 2462: 2429: 2419: 2406: 2396: 2383: 2373: 2360: 2350: 2337: 2327: 2314: 2304: 2285: 2261: 2249: 2235: 2223: 2211: 2199: 2182: 2170: 2156: 2144: 2132: 2120: 2103: 2091: 2077: 2065: 2053: 2041: 2007: 1995: 1983: 1969: 1957: 1945: 1933: 1921: 1907: 1905: 1873: 1860: 1851: 1823: 1810: 1801: 1773: 1760: 1751: 1717:, the relative areas of triangles in any 1619: 1611: 1559: 1551: 1531: 1511: 1491: 1437: 1429: 1386: 1364: 1342: 1318: 1278: 1254: 1214: 1206: 1184: 1160: 1136: 935: 916: 897: 891: 868: 848: 828: 808: 788: 768: 226:is a region of a general two-dimensional 210:, three "straight" segments (having zero 5647:. Dover Publications. pp. 149–160. 5403: 4952: 1595:{\displaystyle s={\tfrac {1}{2}}(a+b+c)} 568:, which is the center of the triangle's 6383:(4th ed.). John Wiley & Sons. 5844:The Thirteen Books of Euclid's Elements 5599:A panoramic view of Riemannian geometry 5327: 4984: 4979: 4964: 4885: 4848:MacTutor History of Mathematics Archive 4169: 4127: 366: 324: 5391: 5002: 4928: 4879: 4808: 4796: 4784: 4772: 4760: 4694: 4666: 4105:shapes based on triangles include the 4094:is characterized by such comparisons. 3774:Of all triangles contained in a given 3708:Figures circumscribed about a triangle 3235:and the triangle has a side of length 2787:{\displaystyle \alpha :\beta :\gamma } 38: 5422:. Yale University Press. p. 21. 4900: 4864: 4722: 4706: 4654: 4638: 4378: 4362: 4350: 4277: 4261: 4216: 4192: 3926:of any pseudotriangle is a triangle. 7: 5671:(facsimile ed.). TASCHEN GmbH. 5253: 4820: 4622: 4539: 4520: 4504: 4488: 4470: 4442: 4332: 4296: 4243: 1238:{\displaystyle T={\tfrac {1}{2}}bh.} 6224:Introduction to Hyperbolic Geometry 5748:Discrete and Computational Geometry 5728:Anneli Lax New Mathematical Library 1079:necessary and sufficient conditions 266:sine, cosine, and tangent functions 187:, and any three points that do not 5470:Anglin, W. S.; Lambek, J. (1995). 5344:Polking, John C. (25 April 1999). 4086:In more general spaces, there are 1701:and area. The locus of their apex 1424:, so the area of the triangle is: 483:; this point is the center of the 276:Definition, terminology, and types 268:relate side lengths and angles in 25: 6087:The American Mathematical Monthly 5954:Jordan, D. W.; Smith, P. (2010). 5277:Vahedi & van der Stappen 2008 5087:Journal for Geometry and Graphics 2578:Triangulation in a simple polygon 2528:Rigidity of a triangle and square 197:three-dimensional Euclidean space 195:. More generally, four points in 189:all lie on the same straight line 6426:Encyclopedia of triangle centers 5039:Kimberling, Clark (March 2008). 3957: 3948: 3725: 3716: 3156: 3147: 2641:triangles that are separated by 1415:{\displaystyle h=a\sin(\gamma )} 630: 621: 533: 524: 423:Encyclopedia of Triangle Centers 397: 383: 369: 355: 341: 327: 47: 5875:Geometry: Our Cultural Heritage 4353:, Definition 20, Definition 21. 2804:Figures inscribed in a triangle 6036:Geometry: A High School Course 5999:10.1080/00029890.2008.11920532 5560:10.1080/0025570X.1998.11996652 5226:10.1080/0025570X.1994.11996212 4050: 4035: 3616:{\displaystyle 2{\sqrt {2}}/3} 2473: 2465: 2435: 2297: 1879: 1853: 1829: 1803: 1779: 1753: 1666: 1654: 1651: 1639: 1636: 1624: 1589: 1571: 1409: 1403: 995: 989: 980: 974: 965: 959: 1: 6295:Geometry from Euclid to Knots 6207:. American Mathematical Soc. 6014:American Mathematical Society 5986:American Mathematical Monthly 5908:American Mathematical Monthly 5800:The Cartoon Guide to Geometry 5773:Real-Time Collision Detection 1885:{\displaystyle (x_{C},y_{C})} 1835:{\displaystyle (x_{B},y_{B})} 1785:{\displaystyle (x_{A},y_{A})} 1102:and then includes ASA above.) 1047:about similar triangles are: 1034:Two triangles are said to be 428:existence of these points is 6315:; Griffin, Jennifer (2008). 5309:Devadoss & O'Rourke 2011 5015:Allaire, Zhou & Yao 2012 3930:Triangle in non-planar space 3809:is a triangle with circular 3117: 3099: 3082: 3064: 3040: 3022: 3005: 2987: 2963: 2945: 2928: 2910: 6413:Encyclopedia of Mathematics 6127:. In Nielsen, Frank (ed.). 5293:Pocchiola & Vegter 1999 5027:Coxeter & Greitzer 1967 4679:Ramsay & Richtmyer 1995 140:sum of angles of a triangle 111:. The corners, also called 7000: 6038:(2nd ed.). Springer. 5770:Ericson, Christer (2005). 5753:Princeton University Press 5643:Eggleston, H. G. (2007) . 5107:Bailey & Detemple 1998 4811:, pp. 65, 72–73, 111. 4306:Usiskin & Griffin 2008 3933: 3790: 3349:, and the triangle's area 2567: 2564:Triangulation of a polygon 2517: 2498: 1110: 1090:surveying by triangulation 420: 29: 6348:10.1007/978-3-540-68405-3 6232:10.1007/978-1-4757-5585-5 6137:10.1007/978-3-030-65459-7 6077:10.1017/S0025557200172249 6044:10.1007/978-1-4757-2022-8 5888:10.1007/978-3-642-14441-7 5700:10.1142/S0218195992000123 5607:10.1007/978-3-642-18245-7 5480:10.1007/978-1-4612-0803-7 5463:10.1017/S0025557200004277 5239:Chandran & Mount 1992 5164:10.1017/S0025557200182087 5057:10.1017/S002555720018249X 4742:Verdiyan & Salas 2007 4599:10.1007/s00025-008-0294-4 1359:and their included angle 1017:Similarity and congruence 87: 46: 32:Triangle (disambiguation) 6367:Mathematical Reflections 6274:Smith, James T. (2000). 6157:The Mathematical Gazette 5522:Algebra and Trigonometry 5187:The Mathematical Gazette 5045:The Mathematical Gazette 4853:University of St Andrews 4427:Anglin & Lambek 1995 3832:. A pseudotriangle is a 3507:{\displaystyle a^{2}=2T} 3369:are related according to 2480:{\displaystyle |\cdot |} 1125:In the Euclidean plane, 208:non-Euclidean geometries 6123:Nielsen, Frank (2021). 6034:; Murrow, Gene (1988). 6006:King, James R. (2021). 5962:Oxford University Press 5597:Berger, Marcel (2002). 5519:Axler, Sheldon (2012). 5126:Oxman & Stupel 2013 5112:Oxman & Stupel 2013 4913:Jordan & Smith 2010 4153:A subset of a plane is 3823:Mohr–Mascheroni theorem 3782:Miscellaneous triangles 2760:Barycentric coordinates 1372:{\displaystyle \gamma } 1069:Two triangles that are 876:{\displaystyle \gamma } 836:{\displaystyle \alpha } 816:{\displaystyle \gamma } 776:{\displaystyle \alpha } 734:trigonometric functions 134:. A triangle has three 6406:Ivanov, A.B. (2001) . 5817:Hann, Michael (2014). 5472:The Heritage of Thales 5350:Geometry of the Sphere 4586:Results in Mathematics 4462:Lang & Murrow 1988 4411:Lang & Murrow 1988 4395:Lang & Murrow 1988 4324:Lang & Murrow 1988 4235:Lang & Murrow 1988 4208:Lang & Murrow 1988 4177:Lang & Murrow 1988 4077: 4057: 3916: 3887: 3858: 3802: 3694: 3671: 3631: 3617: 3582: 3562: 3542: 3508: 3472: 3363: 3343: 3323: 3296: 3276: 3249: 3229: 3135: 2884: 2864: 2844: 2816:shows how to find the 2788: 2750: 2724: 2661: 2635: 2608: 2579: 2529: 2481: 2449: 1886: 1836: 1786: 1715:affine transformations 1710: 1678: 1596: 1540: 1520: 1500: 1471: 1416: 1373: 1351: 1327: 1308: 1287: 1263: 1239: 1193: 1169: 1145: 1122: 1031: 1008: 877: 857: 856:{\displaystyle \beta } 837: 817: 797: 796:{\displaystyle \beta } 777: 727:exterior angle theorem 700: 470:perpendicular bisector 464: 249:sides, for instance a 245:is a shape with three 150:and its interior is a 130:, are one-dimensional 27:Shape with three sides 6257:John Wiley & Sons 5527:John Wiley & Sons 5029:, pp. 18, 23–25. 4867:, Propositions 36–41. 4843:"Heron of Alexandria" 4266:p. 187, Definition 20 4078: 4058: 3922:bitangent lines. The 3917: 3888: 3859: 3800: 3758:Steiner circumellipse 3737:Steiner circumellipse 3695: 3672: 3629: 3618: 3583: 3563: 3543: 3541:{\displaystyle q=a/2} 3509: 3473: 3364: 3344: 3324: 3322:{\displaystyle h_{a}} 3297: 3277: 3275:{\displaystyle q_{a}} 3250: 3230: 3228:{\displaystyle q_{a}} 3136: 2885: 2865: 2845: 2789: 2751: 2725: 2723:{\displaystyle x:y:z} 2696:Trilinear coordinates 2662: 2636: 2609: 2587:polygon triangulation 2577: 2570:Polygon triangulation 2527: 2482: 2450: 1887: 1837: 1787: 1742:Cartesian coordinates 1689: 1679: 1597: 1541: 1521: 1501: 1472: 1417: 1374: 1352: 1328: 1301: 1288: 1264: 1240: 1194: 1170: 1146: 1120: 1024: 1009: 878: 858: 838: 818: 798: 778: 759:, whose vertices are 698: 450: 264:. In particular, the 75:{3} (for equilateral) 6687:Nonagon/Enneagon (9) 6617:Tangential trapezoid 6293:Stahl, Saul (2003). 6252:Geometry For Dummies 6064:Mathematical Gazette 5979:Kalman, Dan (2008). 5547:Mathematics Magazine 5450:Mathematical Gazette 5214:Mathematics Magazine 5152:Mathematical Gazette 4839:Robertson, Edmund F. 4747:Longuet-Higgins 2003 4067: 4019: 3915:{\displaystyle 3n-3} 3897: 3893:pseudotriangles and 3886:{\displaystyle 2n-2} 3868: 3848: 3681: 3661: 3592: 3572: 3552: 3518: 3482: 3373: 3353: 3333: 3306: 3286: 3259: 3239: 3212: 2894: 2874: 2854: 2828: 2818:foci of this ellipse 2766: 2734: 2702: 2645: 2619: 2598: 2461: 1904: 1850: 1800: 1750: 1610: 1550: 1530: 1510: 1490: 1428: 1385: 1363: 1341: 1317: 1277: 1253: 1205: 1183: 1159: 1135: 890: 867: 847: 827: 807: 787: 767: 335:Equilateral triangle 292:equilateral triangle 6799:Megagon (1,000,000) 6567:Isosceles trapezoid 6276:Methods of Geometry 6249:Ryan, Mark (2008). 6188:Forum Geometricorum 5858:Dover reprint, 1956 5853:2027/uva.x001426155 5406:, p. viii+112. 5394:, pp. 134–139. 5140:, pp. 149–160. 4837:O'Connor, John J.; 4763:, pp. 157–167. 4697:, pp. 224–225. 4669:, pp. 107–109. 4088:comparison theorems 3993:hyperbolic triangle 3968:Hyperbolic triangle 3936:Hyperbolic triangle 3746:tangential triangle 2843:{\displaystyle ABC} 2749:{\displaystyle x:y} 2679:Location of a point 2660:{\displaystyle n-3} 2634:{\displaystyle n-2} 2558:tetrahedral trusses 2520:Structural rigidity 2507:triangle inequality 2501:Triangle inequality 1484:Heron of Alexandria 757:degenerate triangle 586:orthocentric system 220:hyperbolic triangle 6769:Icositetragon (24) 6424:Clark Kimberling: 6164:(485 =): 263–274. 5872:Holme, A. (2010). 5802:. William Morrow. 5724:Geometry Revisited 5199:10.1017/mag.2017.2 4195:, pp. xx–xxi. 4073: 4053: 4001:spherical triangle 3989:spherical geometry 3972:spherical triangle 3940:Spherical triangle 3912: 3883: 3854: 3803: 3787:Circular triangles 3693:{\displaystyle 2T} 3690: 3667: 3632: 3613: 3578: 3558: 3538: 3504: 3468: 3359: 3339: 3319: 3292: 3272: 3245: 3225: 3131: 2880: 2860: 2850:, let the foci be 2840: 2784: 2746: 2720: 2657: 2631: 2604: 2580: 2530: 2489:matrix determinant 2477: 2445: 2443: 2295: 2269: 2209: 2190: 2130: 2111: 2051: 2032: 1931: 1882: 1832: 1782: 1738:affine coordinates 1711: 1674: 1592: 1569: 1536: 1516: 1496: 1467: 1447: 1412: 1369: 1347: 1323: 1309: 1283: 1259: 1235: 1224: 1189: 1165: 1141: 1123: 1113:Area of a triangle 1077:Some individually 1032: 1004: 873: 853: 833: 813: 793: 773: 713:parallel postulate 701: 465: 349:Isosceles triangle 296:isosceles triangle 216:spherical triangle 181:Euclidean geometry 174:area of a triangle 6971: 6970: 6812: 6811: 6789:Myriagon (10,000) 6774:Triacontagon (30) 6738:Heptadecagon (17) 6728:Pentadecagon (15) 6723:Tetradecagon (14) 6662:Quadrilateral (4) 6532:Antiparallelogram 6390:978-1-119-32113-2 6357:978-3-540-68405-3 6297:. Prentice-Hall. 6266:978-0-470-08946-0 6241:978-1-4757-5585-5 6214:978-0-8218-0674-6 6146:978-3-030-65458-0 6053:978-1-4757-2022-8 5971:978-0-19-928201-2 5897:978-3-642-14441-7 5830:978-1-4725-8431-1 5823:. A&C Black. 5809:978-0-06-315757-6 5787:978-1-55860-732-3 5762:978-0-691-14553-2 5737:978-0-88385-619-2 5716:Coxeter, H. S. M. 5678:978-3-8365-4471-9 5654:978-0-486-45846-5 5635:978-3-540-65620-3 5616:978-3-642-18245-7 5489:978-1-4612-0803-7 5429:978-0-300-22070-4 5263:Hungerbühler 1994 4657:, Proposition 32. 4107:Sierpiński gasket 4076:{\displaystyle f} 3857:{\displaystyle n} 3819:Reuleaux triangle 3807:circular triangle 3793:Circular triangle 3765:Kiepert hyperbola 3670:{\displaystyle T} 3603: 3581:{\displaystyle a} 3561:{\displaystyle a} 3463: 3423: 3362:{\displaystyle T} 3342:{\displaystyle a} 3295:{\displaystyle a} 3248:{\displaystyle a} 3186:midpoint triangle 3172:Gergonne triangle 3123: 3120: 3102: 3085: 3067: 3046: 3043: 3025: 3008: 2990: 2969: 2966: 2948: 2931: 2913: 2883:{\displaystyle Q} 2863:{\displaystyle P} 2822:Mandart inellipse 2810:Steiner inellipse 2615:sides, there are 2607:{\displaystyle n} 2294: 2208: 2129: 2050: 1930: 1690:Orange triangles 1669: 1568: 1539:{\displaystyle c} 1519:{\displaystyle b} 1499:{\displaystyle a} 1446: 1350:{\displaystyle b} 1326:{\displaystyle a} 1286:{\displaystyle h} 1262:{\displaystyle b} 1223: 1192:{\displaystyle h} 1168:{\displaystyle b} 1144:{\displaystyle 1} 687:of the triangle. 591:nine-point circle 544:Nine-point circle 442:Menelaus' theorem 251:circular triangle 224:geodesic triangle 93: 92: 16:(Redirected from 6991: 6784:Chiliagon (1000) 6764:Icositrigon (23) 6743:Octadecagon (18) 6733:Hexadecagon (16) 6637: 6456: 6449: 6442: 6433: 6421: 6394: 6370: 6361: 6330: 6308: 6289: 6270: 6245: 6218: 6196: 6181: 6150: 6119: 6080: 6057: 6027: 6002: 5975: 5960:(4th ed.). 5950: 5924: 5901: 5856: 5839:Heath, Thomas L. 5834: 5813: 5791: 5766: 5741: 5711: 5682: 5658: 5639: 5620: 5593: 5568:Ballmann, Werner 5563: 5540: 5536:978-0470-58579-5 5515: 5493: 5466: 5434: 5433: 5413: 5407: 5401: 5395: 5389: 5383: 5382: 5380: 5378: 5367: 5361: 5360: 5358: 5356: 5341: 5335: 5325: 5316: 5306: 5300: 5290: 5284: 5274: 5268: 5248: 5242: 5236: 5230: 5229: 5209: 5203: 5202: 5182: 5176: 5175: 5158:(522): 436–452. 5147: 5141: 5135: 5129: 5123: 5117: 5101: 5095: 5094: 5084: 5075: 5069: 5068: 5036: 5030: 5024: 5018: 5012: 5006: 5000: 4994: 4974: 4968: 4962: 4956: 4950: 4944: 4941:Berg et al. 2000 4938: 4932: 4926: 4920: 4910: 4904: 4903:, p. 86–87. 4898: 4892: 4874: 4868: 4862: 4856: 4855: 4834: 4828: 4818: 4812: 4806: 4800: 4794: 4788: 4782: 4776: 4770: 4764: 4758: 4752: 4736: 4730: 4720: 4714: 4704: 4698: 4692: 4686: 4676: 4670: 4664: 4658: 4652: 4646: 4636: 4630: 4620: 4614: 4613: 4580: 4574: 4573: 4553: 4547: 4537: 4528: 4518: 4512: 4502: 4496: 4486: 4480: 4456: 4450: 4440: 4434: 4424: 4418: 4408: 4402: 4392: 4386: 4376: 4370: 4360: 4354: 4348: 4342: 4318: 4312: 4291: 4285: 4275: 4269: 4259: 4253: 4229: 4223: 4202: 4196: 4190: 4184: 4174: 4158: 4151: 4145: 4142: 4136: 4132: 4098:Fractal geometry 4082: 4080: 4079: 4074: 4062: 4060: 4059: 4054: 4031: 4030: 4013:Girard's theorem 3985:hyperbolic space 3961: 3952: 3921: 3919: 3918: 3913: 3892: 3890: 3889: 3884: 3863: 3861: 3860: 3855: 3834:simply-connected 3729: 3720: 3699: 3697: 3696: 3691: 3676: 3674: 3673: 3668: 3646:. In either its 3622: 3620: 3619: 3614: 3609: 3604: 3599: 3587: 3585: 3584: 3579: 3567: 3565: 3564: 3559: 3547: 3545: 3544: 3539: 3534: 3513: 3511: 3510: 3505: 3494: 3493: 3477: 3475: 3474: 3469: 3464: 3462: 3461: 3460: 3444: 3443: 3442: 3429: 3424: 3422: 3412: 3411: 3401: 3390: 3385: 3384: 3368: 3366: 3365: 3360: 3348: 3346: 3345: 3340: 3328: 3326: 3325: 3320: 3318: 3317: 3301: 3299: 3298: 3293: 3281: 3279: 3278: 3273: 3271: 3270: 3254: 3252: 3251: 3246: 3234: 3232: 3231: 3226: 3224: 3223: 3197:extouch triangle 3193:intouch triangle 3160: 3151: 3140: 3138: 3137: 3132: 3124: 3122: 3121: 3116: 3108: 3103: 3098: 3090: 3087: 3086: 3081: 3073: 3068: 3063: 3055: 3052: 3047: 3045: 3044: 3039: 3031: 3026: 3021: 3013: 3010: 3009: 3004: 2996: 2991: 2986: 2978: 2975: 2970: 2968: 2967: 2962: 2954: 2949: 2944: 2936: 2933: 2932: 2927: 2919: 2914: 2909: 2901: 2898: 2889: 2887: 2886: 2881: 2869: 2867: 2866: 2861: 2849: 2847: 2846: 2841: 2814:Marden's theorem 2793: 2791: 2790: 2785: 2755: 2753: 2752: 2747: 2729: 2727: 2726: 2721: 2673:two ears theorem 2666: 2664: 2663: 2658: 2640: 2638: 2637: 2632: 2614: 2613: 2611: 2610: 2605: 2486: 2484: 2483: 2478: 2476: 2468: 2454: 2452: 2451: 2446: 2444: 2434: 2433: 2424: 2423: 2411: 2410: 2401: 2400: 2388: 2387: 2378: 2377: 2365: 2364: 2355: 2354: 2342: 2341: 2332: 2331: 2319: 2318: 2309: 2308: 2296: 2287: 2278: 2274: 2273: 2266: 2265: 2254: 2253: 2240: 2239: 2228: 2227: 2210: 2201: 2195: 2194: 2187: 2186: 2175: 2174: 2161: 2160: 2149: 2148: 2131: 2122: 2116: 2115: 2108: 2107: 2096: 2095: 2082: 2081: 2070: 2069: 2052: 2043: 2037: 2036: 2012: 2011: 2000: 1999: 1988: 1987: 1974: 1973: 1962: 1961: 1950: 1949: 1932: 1923: 1896:shoelace formula 1893: 1891: 1889: 1888: 1883: 1878: 1877: 1865: 1864: 1843: 1841: 1839: 1838: 1833: 1828: 1827: 1815: 1814: 1793: 1791: 1789: 1788: 1783: 1778: 1777: 1765: 1764: 1707:Lexell's theorem 1704: 1700: 1696: 1683: 1681: 1680: 1675: 1670: 1620: 1601: 1599: 1598: 1593: 1570: 1561: 1545: 1543: 1542: 1537: 1525: 1523: 1522: 1517: 1505: 1503: 1502: 1497: 1476: 1474: 1473: 1468: 1448: 1439: 1423: 1421: 1419: 1418: 1413: 1378: 1376: 1375: 1370: 1358: 1356: 1354: 1353: 1348: 1334: 1332: 1330: 1329: 1324: 1307: 1294: 1292: 1290: 1289: 1284: 1270: 1268: 1266: 1265: 1260: 1244: 1242: 1241: 1236: 1225: 1216: 1200: 1198: 1196: 1195: 1190: 1176: 1174: 1172: 1171: 1166: 1152: 1150: 1148: 1147: 1142: 1026:with B'C'. Note 1013: 1011: 1010: 1005: 940: 939: 921: 920: 902: 901: 882: 880: 879: 874: 862: 860: 859: 854: 842: 840: 839: 834: 822: 820: 819: 814: 802: 800: 799: 794: 782: 780: 779: 774: 634: 625: 604:) and the three 537: 528: 401: 387: 373: 362:Scalene triangle 359: 345: 331: 300:scalene triangle 242: 241: 142:always equals a 85:various methods; 51: 39: 21: 6999: 6998: 6994: 6993: 6992: 6990: 6989: 6988: 6974: 6973: 6972: 6967: 6866: 6820: 6808: 6752: 6718:Tridecagon (13) 6708:Hendecagon (11) 6696: 6632: 6626: 6597:Right trapezoid 6518: 6470: 6460: 6405: 6402: 6397: 6391: 6373: 6364: 6358: 6333: 6327: 6313:Usiskin, Zalman 6311: 6305: 6292: 6286: 6273: 6267: 6248: 6242: 6221: 6215: 6199: 6184: 6170:10.2307/3618298 6153: 6147: 6122: 6100:10.2307/2319703 6083: 6060: 6054: 6030: 6024: 6005: 5978: 5972: 5953: 5931:10.2307/2974536 5904: 5898: 5871: 5837: 5831: 5816: 5810: 5794: 5788: 5769: 5763: 5744: 5738: 5720:Greitzer, S. L. 5714: 5685: 5679: 5661: 5655: 5642: 5636: 5623: 5617: 5596: 5582: 5566: 5543: 5537: 5518: 5512: 5498:Apostol, Tom M. 5496: 5490: 5469: 5446: 5442: 5437: 5430: 5415: 5414: 5410: 5402: 5398: 5390: 5386: 5376: 5374: 5369: 5368: 5364: 5354: 5352: 5343: 5342: 5338: 5326: 5319: 5307: 5303: 5291: 5287: 5275: 5271: 5267: 5249: 5245: 5237: 5233: 5211: 5210: 5206: 5184: 5183: 5179: 5149: 5148: 5144: 5136: 5132: 5124: 5120: 5116: 5102: 5098: 5082: 5077: 5076: 5072: 5038: 5037: 5033: 5025: 5021: 5013: 5009: 5001: 4997: 4993: 4975: 4971: 4963: 4959: 4951: 4947: 4939: 4935: 4927: 4923: 4911: 4907: 4899: 4895: 4891: 4888:, p. 34–35 4875: 4871: 4863: 4859: 4836: 4835: 4831: 4819: 4815: 4807: 4803: 4795: 4791: 4783: 4779: 4771: 4767: 4759: 4755: 4751: 4737: 4733: 4721: 4717: 4705: 4701: 4693: 4689: 4677: 4673: 4665: 4661: 4653: 4649: 4637: 4633: 4621: 4617: 4582: 4581: 4577: 4570: 4555: 4554: 4550: 4538: 4531: 4519: 4515: 4503: 4499: 4487: 4483: 4479: 4457: 4453: 4441: 4437: 4425: 4421: 4409: 4405: 4393: 4389: 4377: 4373: 4361: 4357: 4349: 4345: 4341: 4319: 4315: 4311: 4292: 4288: 4276: 4272: 4260: 4256: 4252: 4230: 4226: 4222: 4219:, Definition 20 4203: 4199: 4191: 4187: 4175: 4171: 4167: 4162: 4161: 4152: 4148: 4143: 4139: 4133: 4129: 4124: 4119: 4100: 4065: 4064: 4022: 4017: 4016: 3981:Euclidean space 3977: 3976: 3975: 3974: 3964: 3963: 3962: 3954: 3953: 3942: 3934:Main articles: 3932: 3895: 3894: 3866: 3865: 3846: 3845: 3842:bitangent lines 3795: 3789: 3784: 3742: 3741: 3740: 3739: 3732: 3731: 3730: 3722: 3721: 3710: 3679: 3678: 3659: 3658: 3644:symmedian point 3636:Lemoine hexagon 3590: 3589: 3570: 3569: 3550: 3549: 3516: 3515: 3485: 3480: 3479: 3452: 3445: 3434: 3430: 3403: 3402: 3391: 3376: 3371: 3370: 3351: 3350: 3331: 3330: 3309: 3304: 3303: 3284: 3283: 3262: 3257: 3256: 3237: 3236: 3215: 3210: 3209: 3177: 3176: 3175: 3174: 3163: 3162: 3161: 3153: 3152: 3109: 3091: 3088: 3074: 3056: 3053: 3032: 3014: 3011: 2997: 2979: 2976: 2955: 2937: 2934: 2920: 2902: 2899: 2892: 2891: 2872: 2871: 2852: 2851: 2826: 2825: 2806: 2801: 2799:Related figures 2764: 2763: 2732: 2731: 2700: 2699: 2685:Cartesian plane 2681: 2643: 2642: 2617: 2616: 2596: 2595: 2594: 2572: 2566: 2522: 2516: 2503: 2497: 2459: 2458: 2442: 2441: 2425: 2415: 2402: 2392: 2379: 2369: 2356: 2346: 2333: 2323: 2310: 2300: 2276: 2275: 2268: 2267: 2257: 2255: 2245: 2242: 2241: 2231: 2229: 2219: 2212: 2189: 2188: 2178: 2176: 2166: 2163: 2162: 2152: 2150: 2140: 2133: 2110: 2109: 2099: 2097: 2087: 2084: 2083: 2073: 2071: 2061: 2054: 2031: 2030: 2025: 2020: 2014: 2013: 2003: 2001: 1991: 1989: 1979: 1976: 1975: 1965: 1963: 1953: 1951: 1941: 1934: 1914: 1902: 1901: 1869: 1856: 1848: 1847: 1845: 1819: 1806: 1798: 1797: 1795: 1769: 1756: 1748: 1747: 1745: 1702: 1698: 1691: 1608: 1607: 1548: 1547: 1528: 1527: 1508: 1507: 1488: 1487: 1480:Heron's formula 1426: 1425: 1383: 1382: 1380: 1361: 1360: 1339: 1338: 1336: 1315: 1314: 1312: 1303: 1275: 1274: 1272: 1251: 1250: 1248: 1203: 1202: 1181: 1180: 1178: 1157: 1156: 1154: 1133: 1132: 1130: 1115: 1109: 1019: 931: 912: 893: 888: 887: 865: 864: 845: 844: 825: 824: 805: 804: 785: 784: 765: 764: 738:sine and cosine 709:Euclidean space 693: 684:symmedian point 647: 646: 645: 644: 637: 636: 635: 627: 626: 602:Feuerbach point 554: 553: 552: 551: 540: 539: 538: 530: 529: 491:Thales' theorem 425: 419: 414: 407: 405:Obtuse triangle 402: 393: 388: 379: 374: 363: 360: 351: 346: 337: 332: 316:obtuse triangle 278: 270:right triangles 239: 238: 136:internal angles 86: 71:Schläfli symbol 35: 28: 23: 22: 15: 12: 11: 5: 6997: 6995: 6987: 6986: 6976: 6975: 6969: 6968: 6966: 6965: 6960: 6955: 6950: 6945: 6940: 6935: 6930: 6925: 6923:Pseudotriangle 6920: 6915: 6910: 6905: 6900: 6895: 6890: 6885: 6880: 6874: 6872: 6868: 6867: 6865: 6864: 6859: 6854: 6849: 6844: 6839: 6834: 6829: 6823: 6821: 6814: 6813: 6810: 6809: 6807: 6806: 6801: 6796: 6791: 6786: 6781: 6776: 6771: 6766: 6760: 6758: 6754: 6753: 6751: 6750: 6745: 6740: 6735: 6730: 6725: 6720: 6715: 6713:Dodecagon (12) 6710: 6704: 6702: 6698: 6697: 6695: 6694: 6689: 6684: 6679: 6674: 6669: 6664: 6659: 6654: 6649: 6643: 6641: 6634: 6628: 6627: 6625: 6624: 6619: 6614: 6609: 6604: 6599: 6594: 6589: 6584: 6579: 6574: 6569: 6564: 6559: 6554: 6549: 6544: 6539: 6534: 6528: 6526: 6524:Quadrilaterals 6520: 6519: 6517: 6516: 6511: 6506: 6501: 6496: 6491: 6486: 6480: 6478: 6472: 6471: 6461: 6459: 6458: 6451: 6444: 6436: 6430: 6429: 6422: 6401: 6400:External links 6398: 6396: 6395: 6389: 6375:Young, Cynthia 6371: 6362: 6356: 6331: 6325: 6309: 6303: 6290: 6284: 6271: 6265: 6246: 6240: 6219: 6213: 6197: 6182: 6151: 6145: 6120: 6094:(6): 648–651. 6081: 6058: 6052: 6028: 6022: 6003: 5993:(4): 330–338. 5976: 5970: 5951: 5922:10.1.1.45.9902 5915:(8): 784–787. 5902: 5896: 5869: 5835: 5829: 5814: 5808: 5792: 5786: 5767: 5761: 5742: 5736: 5712: 5694:(2): 191–214. 5683: 5677: 5659: 5653: 5640: 5634: 5621: 5615: 5594: 5580: 5564: 5554:(4): 278–284. 5541: 5535: 5516: 5510: 5502:Linear Algebra 5494: 5488: 5467: 5443: 5441: 5438: 5436: 5435: 5428: 5408: 5396: 5384: 5362: 5336: 5317: 5301: 5285: 5269: 5266: 5265: 5260: 5250: 5243: 5231: 5220:(3): 188–205. 5204: 5193:(550): 11–26. 5177: 5142: 5138:Eggleston 2007 5130: 5118: 5115: 5114: 5109: 5103: 5096: 5070: 5051:(523): 29–38. 5031: 5019: 5007: 4995: 4992: 4991: 4982: 4976: 4969: 4957: 4945: 4933: 4931:, p. 125. 4921: 4905: 4893: 4890: 4889: 4883: 4876: 4869: 4857: 4829: 4813: 4801: 4789: 4787:, p. 171. 4777: 4775:, p. 167. 4765: 4753: 4750: 4749: 4744: 4738: 4731: 4715: 4699: 4687: 4671: 4659: 4647: 4631: 4615: 4593:(1–2): 41–50. 4575: 4569:978-0883850992 4568: 4548: 4529: 4513: 4497: 4481: 4478: 4477: 4468: 4458: 4451: 4435: 4419: 4403: 4387: 4371: 4355: 4343: 4340: 4339: 4330: 4320: 4313: 4310: 4309: 4303: 4293: 4286: 4270: 4254: 4251: 4250: 4241: 4231: 4224: 4221: 4220: 4214: 4204: 4197: 4185: 4168: 4166: 4163: 4160: 4159: 4146: 4137: 4126: 4125: 4123: 4120: 4118: 4115: 4111:Koch snowflake 4099: 4096: 4072: 4052: 4049: 4046: 4043: 4040: 4037: 4034: 4029: 4025: 3997:saddle surface 3966: 3965: 3956: 3955: 3947: 3946: 3945: 3944: 3943: 3931: 3928: 3911: 3908: 3905: 3902: 3882: 3879: 3876: 3873: 3853: 3830:pseudotriangle 3791:Main article: 3788: 3785: 3783: 3780: 3776:convex polygon 3767:is the unique 3734: 3733: 3724: 3723: 3715: 3714: 3713: 3712: 3711: 3709: 3706: 3689: 3686: 3666: 3655:convex polygon 3640:cyclic hexagon 3612: 3608: 3602: 3597: 3577: 3557: 3537: 3533: 3529: 3526: 3523: 3503: 3500: 3497: 3492: 3488: 3467: 3459: 3455: 3451: 3448: 3441: 3437: 3433: 3427: 3421: 3418: 3415: 3410: 3406: 3400: 3397: 3394: 3388: 3383: 3379: 3358: 3338: 3329:from the side 3316: 3312: 3291: 3269: 3265: 3244: 3222: 3218: 3181:pedal triangle 3168:pedal triangle 3165: 3164: 3155: 3154: 3146: 3145: 3144: 3143: 3142: 3130: 3127: 3119: 3115: 3112: 3106: 3101: 3097: 3094: 3084: 3080: 3077: 3071: 3066: 3062: 3059: 3050: 3042: 3038: 3035: 3029: 3024: 3020: 3017: 3007: 3003: 3000: 2994: 2989: 2985: 2982: 2973: 2965: 2961: 2958: 2952: 2947: 2943: 2940: 2930: 2926: 2923: 2917: 2912: 2908: 2905: 2879: 2859: 2839: 2836: 2833: 2805: 2802: 2800: 2797: 2796: 2795: 2783: 2780: 2777: 2774: 2771: 2757: 2745: 2742: 2739: 2719: 2716: 2713: 2710: 2707: 2680: 2677: 2656: 2653: 2650: 2630: 2627: 2624: 2603: 2591:simple polygon 2568:Main article: 2565: 2562: 2518:Main article: 2515: 2512: 2499:Main article: 2496: 2493: 2475: 2471: 2467: 2440: 2437: 2432: 2428: 2422: 2418: 2414: 2409: 2405: 2399: 2395: 2391: 2386: 2382: 2376: 2372: 2368: 2363: 2359: 2353: 2349: 2345: 2340: 2336: 2330: 2326: 2322: 2317: 2313: 2307: 2303: 2299: 2293: 2290: 2284: 2281: 2279: 2277: 2272: 2264: 2260: 2256: 2252: 2248: 2244: 2243: 2238: 2234: 2230: 2226: 2222: 2218: 2217: 2215: 2207: 2204: 2198: 2193: 2185: 2181: 2177: 2173: 2169: 2165: 2164: 2159: 2155: 2151: 2147: 2143: 2139: 2138: 2136: 2128: 2125: 2119: 2114: 2106: 2102: 2098: 2094: 2090: 2086: 2085: 2080: 2076: 2072: 2068: 2064: 2060: 2059: 2057: 2049: 2046: 2040: 2035: 2029: 2026: 2024: 2021: 2019: 2016: 2015: 2010: 2006: 2002: 1998: 1994: 1990: 1986: 1982: 1978: 1977: 1972: 1968: 1964: 1960: 1956: 1952: 1948: 1944: 1940: 1939: 1937: 1929: 1926: 1920: 1917: 1915: 1913: 1910: 1909: 1881: 1876: 1872: 1868: 1863: 1859: 1855: 1831: 1826: 1822: 1818: 1813: 1809: 1805: 1781: 1776: 1772: 1768: 1763: 1759: 1755: 1673: 1668: 1665: 1662: 1659: 1656: 1653: 1650: 1647: 1644: 1641: 1638: 1635: 1632: 1629: 1626: 1623: 1618: 1615: 1591: 1588: 1585: 1582: 1579: 1576: 1573: 1567: 1564: 1558: 1555: 1535: 1515: 1495: 1482:, named after 1466: 1463: 1460: 1457: 1454: 1451: 1445: 1442: 1436: 1433: 1411: 1408: 1405: 1402: 1399: 1396: 1393: 1390: 1368: 1346: 1322: 1282: 1258: 1234: 1231: 1228: 1222: 1219: 1213: 1210: 1188: 1164: 1140: 1111:Main article: 1108: 1105: 1104: 1103: 1096: 1093: 1086: 1067: 1066: 1063: 1060:included angle 1055: 1052:If and only if 1018: 1015: 1003: 1000: 997: 994: 991: 988: 985: 982: 979: 976: 973: 970: 967: 964: 961: 958: 955: 952: 949: 946: 943: 938: 934: 930: 927: 924: 919: 915: 911: 908: 905: 900: 896: 885:if and only if 872: 852: 832: 812: 792: 772: 750:law of cosines 718:exterior angle 692: 689: 673:center of mass 639: 638: 629: 628: 620: 619: 618: 617: 616: 559:angle bisector 542: 541: 532: 531: 523: 522: 521: 520: 519: 430:Ceva's theorem 421:Main article: 418: 415: 413: 410: 409: 408: 403: 396: 394: 391:Acute triangle 389: 382: 380: 377:Right triangle 375: 368: 365: 364: 361: 354: 352: 347: 340: 338: 333: 326: 312:acute triangle 308:right triangle 277: 274: 144:straight angle 91: 90: 83: 77: 76: 73: 67: 66: 63: 53: 52: 44: 43: 26: 24: 14: 13: 10: 9: 6: 4: 3: 2: 6996: 6985: 6982: 6981: 6979: 6964: 6963:Weakly simple 6961: 6959: 6956: 6954: 6951: 6949: 6946: 6944: 6941: 6939: 6936: 6934: 6931: 6929: 6926: 6924: 6921: 6919: 6916: 6914: 6911: 6909: 6906: 6904: 6903:Infinite skew 6901: 6899: 6896: 6894: 6891: 6889: 6886: 6884: 6881: 6879: 6876: 6875: 6873: 6869: 6863: 6860: 6858: 6855: 6853: 6850: 6848: 6845: 6843: 6840: 6838: 6835: 6833: 6830: 6828: 6825: 6824: 6822: 6819: 6818:Star polygons 6815: 6805: 6804:Apeirogon (∞) 6802: 6800: 6797: 6795: 6792: 6790: 6787: 6785: 6782: 6780: 6777: 6775: 6772: 6770: 6767: 6765: 6762: 6761: 6759: 6755: 6749: 6748:Icosagon (20) 6746: 6744: 6741: 6739: 6736: 6734: 6731: 6729: 6726: 6724: 6721: 6719: 6716: 6714: 6711: 6709: 6706: 6705: 6703: 6699: 6693: 6690: 6688: 6685: 6683: 6680: 6678: 6675: 6673: 6670: 6668: 6665: 6663: 6660: 6658: 6655: 6653: 6650: 6648: 6645: 6644: 6642: 6638: 6635: 6629: 6623: 6620: 6618: 6615: 6613: 6610: 6608: 6605: 6603: 6600: 6598: 6595: 6593: 6590: 6588: 6585: 6583: 6582:Parallelogram 6580: 6578: 6577:Orthodiagonal 6575: 6573: 6570: 6568: 6565: 6563: 6560: 6558: 6557:Ex-tangential 6555: 6553: 6550: 6548: 6545: 6543: 6540: 6538: 6535: 6533: 6530: 6529: 6527: 6525: 6521: 6515: 6512: 6510: 6507: 6505: 6502: 6500: 6497: 6495: 6492: 6490: 6487: 6485: 6482: 6481: 6479: 6477: 6473: 6468: 6464: 6457: 6452: 6450: 6445: 6443: 6438: 6437: 6434: 6427: 6423: 6419: 6415: 6414: 6409: 6404: 6403: 6399: 6392: 6386: 6382: 6381: 6376: 6372: 6368: 6363: 6359: 6353: 6349: 6345: 6341: 6337: 6332: 6328: 6326:9781607526001 6322: 6318: 6314: 6310: 6306: 6304:0-13-032927-4 6300: 6296: 6291: 6287: 6285:0-471-25183-6 6281: 6277: 6272: 6268: 6262: 6258: 6254: 6253: 6247: 6243: 6237: 6233: 6229: 6225: 6220: 6216: 6210: 6206: 6205: 6198: 6194: 6190: 6189: 6183: 6179: 6175: 6171: 6167: 6163: 6159: 6158: 6152: 6148: 6142: 6138: 6134: 6130: 6126: 6121: 6117: 6113: 6109: 6105: 6101: 6097: 6093: 6089: 6088: 6082: 6078: 6074: 6070: 6066: 6065: 6059: 6055: 6049: 6045: 6041: 6037: 6033: 6029: 6025: 6023:9781470464431 6019: 6015: 6011: 6010: 6004: 6000: 5996: 5992: 5988: 5987: 5982: 5977: 5973: 5967: 5963: 5959: 5958: 5952: 5948: 5944: 5940: 5936: 5932: 5928: 5923: 5918: 5914: 5910: 5909: 5903: 5899: 5893: 5889: 5885: 5881: 5877: 5876: 5870: 5867: 5863: 5859: 5854: 5850: 5846: 5845: 5840: 5836: 5832: 5826: 5822: 5821: 5815: 5811: 5805: 5801: 5797: 5796:Gonick, Larry 5793: 5789: 5783: 5779: 5775: 5774: 5768: 5764: 5758: 5754: 5750: 5749: 5743: 5739: 5733: 5729: 5725: 5721: 5717: 5713: 5709: 5705: 5701: 5697: 5693: 5689: 5684: 5680: 5674: 5670: 5669: 5664: 5663:Byrne, Oliver 5660: 5656: 5650: 5646: 5641: 5637: 5631: 5627: 5622: 5618: 5612: 5608: 5604: 5600: 5595: 5591: 5587: 5583: 5581:3-7643-5242-6 5577: 5573: 5569: 5565: 5561: 5557: 5553: 5549: 5548: 5542: 5538: 5532: 5528: 5524: 5523: 5517: 5513: 5511:0-471-17421-1 5507: 5503: 5499: 5495: 5491: 5485: 5481: 5477: 5473: 5468: 5464: 5460: 5456: 5452: 5451: 5445: 5444: 5439: 5431: 5425: 5421: 5420: 5412: 5409: 5405: 5404:Ballmann 1995 5400: 5397: 5393: 5388: 5385: 5373: 5366: 5363: 5351: 5347: 5340: 5337: 5333: 5329: 5324: 5322: 5318: 5314: 5310: 5305: 5302: 5298: 5294: 5289: 5286: 5282: 5278: 5273: 5270: 5264: 5261: 5259: 5255: 5252: 5251: 5247: 5244: 5240: 5235: 5232: 5227: 5223: 5219: 5215: 5208: 5205: 5200: 5196: 5192: 5188: 5181: 5178: 5173: 5169: 5165: 5161: 5157: 5153: 5146: 5143: 5139: 5134: 5131: 5127: 5122: 5119: 5113: 5110: 5108: 5105: 5104: 5100: 5097: 5092: 5088: 5081: 5074: 5071: 5066: 5062: 5058: 5054: 5050: 5046: 5042: 5035: 5032: 5028: 5023: 5020: 5016: 5011: 5008: 5004: 4999: 4996: 4990: 4986: 4983: 4981: 4978: 4977: 4973: 4970: 4966: 4961: 4958: 4954: 4953:Meisters 1975 4949: 4946: 4942: 4937: 4934: 4930: 4925: 4922: 4918: 4914: 4909: 4906: 4902: 4897: 4894: 4887: 4884: 4881: 4878: 4877: 4873: 4870: 4866: 4861: 4858: 4854: 4850: 4849: 4844: 4840: 4833: 4830: 4826: 4822: 4817: 4814: 4810: 4805: 4802: 4799:, p. 64. 4798: 4793: 4790: 4786: 4781: 4778: 4774: 4769: 4766: 4762: 4757: 4754: 4748: 4745: 4743: 4740: 4739: 4735: 4732: 4728: 4724: 4719: 4716: 4712: 4708: 4703: 4700: 4696: 4691: 4688: 4684: 4680: 4675: 4672: 4668: 4663: 4660: 4656: 4651: 4648: 4644: 4640: 4635: 4632: 4628: 4624: 4619: 4616: 4612: 4608: 4604: 4600: 4596: 4592: 4588: 4587: 4579: 4576: 4571: 4565: 4561: 4560: 4552: 4549: 4545: 4541: 4536: 4534: 4530: 4526: 4522: 4517: 4514: 4510: 4506: 4501: 4498: 4494: 4490: 4485: 4482: 4476: 4472: 4469: 4467: 4463: 4460: 4459: 4455: 4452: 4448: 4444: 4439: 4436: 4432: 4428: 4423: 4420: 4416: 4412: 4407: 4404: 4400: 4399:126–127 4396: 4391: 4388: 4384: 4380: 4375: 4372: 4368: 4364: 4359: 4356: 4352: 4347: 4344: 4338: 4334: 4331: 4329: 4325: 4322: 4321: 4317: 4314: 4307: 4304: 4302: 4298: 4295: 4294: 4290: 4287: 4283: 4279: 4274: 4271: 4267: 4263: 4258: 4255: 4249: 4245: 4242: 4240: 4236: 4233: 4232: 4228: 4225: 4218: 4215: 4213: 4209: 4206: 4205: 4201: 4198: 4194: 4189: 4186: 4182: 4178: 4173: 4170: 4164: 4156: 4150: 4147: 4141: 4138: 4131: 4128: 4121: 4116: 4114: 4112: 4108: 4104: 4097: 4095: 4093: 4089: 4084: 4070: 4047: 4044: 4041: 4038: 4032: 4027: 4023: 4014: 4008: 4006: 4002: 3998: 3994: 3990: 3986: 3982: 3973: 3969: 3960: 3951: 3941: 3937: 3929: 3927: 3925: 3909: 3906: 3903: 3900: 3880: 3877: 3874: 3871: 3851: 3843: 3839: 3835: 3831: 3826: 3824: 3820: 3816: 3812: 3808: 3799: 3794: 3786: 3781: 3779: 3777: 3772: 3770: 3766: 3761: 3759: 3753: 3751: 3750:tangent lines 3747: 3738: 3728: 3719: 3707: 3705: 3703: 3702:parallelogram 3687: 3684: 3664: 3656: 3651: 3649: 3645: 3641: 3637: 3628: 3624: 3610: 3606: 3600: 3595: 3575: 3555: 3535: 3531: 3527: 3524: 3521: 3501: 3498: 3495: 3490: 3486: 3465: 3457: 3453: 3449: 3446: 3439: 3435: 3431: 3425: 3419: 3416: 3413: 3408: 3404: 3398: 3395: 3392: 3386: 3381: 3377: 3356: 3336: 3314: 3310: 3289: 3267: 3263: 3242: 3220: 3216: 3206: 3200: 3198: 3194: 3189: 3187: 3182: 3173: 3169: 3159: 3150: 3141: 3128: 3125: 3113: 3110: 3104: 3095: 3092: 3078: 3075: 3069: 3060: 3057: 3048: 3036: 3033: 3027: 3018: 3015: 3001: 2998: 2992: 2983: 2980: 2971: 2959: 2956: 2950: 2941: 2938: 2924: 2921: 2915: 2906: 2903: 2877: 2857: 2837: 2834: 2831: 2823: 2819: 2815: 2811: 2803: 2798: 2781: 2778: 2775: 2772: 2769: 2761: 2758: 2743: 2740: 2737: 2717: 2714: 2711: 2708: 2705: 2697: 2694: 2693: 2692: 2688: 2686: 2678: 2676: 2674: 2670: 2654: 2651: 2648: 2628: 2625: 2622: 2601: 2592: 2588: 2584: 2583:Triangulation 2576: 2571: 2563: 2561: 2559: 2555: 2554:cantilevering 2551: 2547: 2543: 2538: 2535: 2534:parallelogram 2526: 2521: 2513: 2511: 2508: 2502: 2494: 2492: 2490: 2469: 2455: 2438: 2430: 2426: 2420: 2416: 2412: 2407: 2403: 2397: 2393: 2389: 2384: 2380: 2374: 2370: 2366: 2361: 2357: 2351: 2347: 2343: 2338: 2334: 2328: 2324: 2320: 2315: 2311: 2305: 2301: 2291: 2288: 2282: 2280: 2270: 2262: 2258: 2250: 2246: 2236: 2232: 2224: 2220: 2213: 2205: 2202: 2196: 2191: 2183: 2179: 2171: 2167: 2157: 2153: 2145: 2141: 2134: 2126: 2123: 2117: 2112: 2104: 2100: 2092: 2088: 2078: 2074: 2066: 2062: 2055: 2047: 2044: 2038: 2033: 2027: 2022: 2017: 2008: 2004: 1996: 1992: 1984: 1980: 1970: 1966: 1958: 1954: 1946: 1942: 1935: 1927: 1924: 1918: 1916: 1911: 1899: 1897: 1874: 1870: 1866: 1861: 1857: 1824: 1820: 1816: 1811: 1807: 1774: 1770: 1766: 1761: 1757: 1743: 1739: 1734: 1732: 1728: 1727:parallelogram 1724: 1723:oriented area 1720: 1716: 1708: 1697:share a base 1695: 1688: 1684: 1671: 1663: 1660: 1657: 1648: 1645: 1642: 1633: 1630: 1627: 1621: 1616: 1613: 1605: 1604:semiperimeter 1586: 1583: 1580: 1577: 1574: 1565: 1562: 1556: 1553: 1533: 1513: 1493: 1485: 1481: 1477: 1464: 1461: 1458: 1455: 1452: 1449: 1443: 1440: 1434: 1431: 1406: 1400: 1397: 1394: 1391: 1388: 1366: 1344: 1320: 1311:If two sides 1306: 1300: 1296: 1280: 1256: 1245: 1232: 1229: 1226: 1220: 1217: 1211: 1208: 1186: 1162: 1138: 1128: 1119: 1114: 1106: 1101: 1097: 1094: 1091: 1087: 1084: 1083: 1082: 1080: 1075: 1072: 1064: 1061: 1056: 1053: 1050: 1049: 1048: 1046: 1041: 1039: 1038: 1029: 1023: 1016: 1014: 1001: 998: 992: 986: 983: 977: 971: 968: 962: 956: 953: 950: 947: 944: 941: 936: 932: 928: 925: 922: 917: 913: 909: 906: 903: 898: 894: 886: 870: 850: 830: 810: 790: 770: 762: 758: 753: 751: 747: 743: 739: 735: 730: 728: 724: 723:supplementary 720: 719: 714: 710: 706: 697: 690: 688: 686: 685: 680: 679: 674: 670: 669: 664: 660: 659: 654: 653: 643: 633: 624: 615: 613: 612: 607: 603: 599: 598: 593: 592: 587: 583: 582: 577: 573: 572: 567: 566: 561: 560: 549: 545: 536: 527: 518: 516: 515: 510: 506: 502: 501: 495: 492: 488: 487: 482: 481: 476: 472: 471: 462: 458: 454: 449: 445: 443: 439: 435: 431: 424: 416: 411: 406: 400: 395: 392: 386: 381: 378: 372: 367: 358: 353: 350: 344: 339: 336: 330: 325: 323: 321: 317: 313: 309: 305: 301: 297: 293: 288: 286: 285: 275: 273: 271: 267: 263: 258: 256: 252: 248: 244: 235: 234: 229: 225: 221: 217: 213: 209: 204: 202: 198: 194: 190: 186: 185:straight line 182: 177: 175: 171: 170: 165: 164: 159: 158: 153: 152:planar region 149: 145: 141: 137: 133: 132:line segments 129: 128: 123: 120: 116: 115: 110: 106: 102: 98: 89: 84: 82: 78: 74: 72: 68: 64: 62: 58: 54: 50: 45: 40: 37: 33: 19: 6757:>20 sides 6692:Decagon (10) 6677:Heptagon (7) 6667:Pentagon (5) 6657:Triangle (3) 6656: 6552:Equidiagonal 6475: 6411: 6380:Trigonometry 6379: 6366: 6339: 6316: 6294: 6275: 6251: 6226:. Springer. 6223: 6202: 6192: 6186: 6161: 6155: 6128: 6091: 6085: 6068: 6062: 6035: 6008: 5990: 5984: 5956: 5912: 5906: 5874: 5843: 5819: 5799: 5772: 5747: 5723: 5691: 5687: 5667: 5644: 5625: 5601:. Springer. 5598: 5571: 5551: 5545: 5521: 5501: 5474:. Springer. 5471: 5454: 5448: 5418: 5411: 5399: 5387: 5375:. Retrieved 5370:Wood, John. 5365: 5353:. Retrieved 5349: 5339: 5328:Nielsen 2021 5304: 5288: 5272: 5246: 5234: 5217: 5213: 5207: 5190: 5186: 5180: 5155: 5151: 5145: 5133: 5121: 5099: 5090: 5086: 5073: 5048: 5044: 5034: 5022: 5010: 4998: 4985:Ericson 2005 4980:Oldknow 1995 4972: 4965:Oldknow 1995 4960: 4948: 4936: 4924: 4908: 4896: 4886:Apostol 1997 4882:, p. 80 4872: 4860: 4846: 4832: 4816: 4804: 4792: 4780: 4768: 4756: 4734: 4718: 4702: 4690: 4674: 4662: 4650: 4634: 4618: 4610: 4590: 4584: 4578: 4558: 4551: 4516: 4500: 4484: 4454: 4438: 4422: 4406: 4390: 4374: 4358: 4346: 4316: 4289: 4273: 4257: 4227: 4200: 4188: 4172: 4149: 4140: 4130: 4101: 4092:CAT(k) space 4085: 4009: 3978: 3837: 3827: 3804: 3773: 3762: 3754: 3743: 3652: 3633: 3568:is equal to 3204: 3201: 3190: 3178: 2807: 2762:of the form 2689: 2682: 2581: 2542:tessellating 2539: 2531: 2504: 2456: 1900: 1735: 1730: 1719:affine plane 1712: 1693: 1478: 1310: 1304: 1246: 1124: 1099: 1076: 1068: 1059: 1042: 1035: 1033: 754: 746:law of sines 731: 716: 702: 682: 676: 666: 656: 650: 648: 611:Euler's line 609: 595: 589: 579: 575: 569: 563: 557: 555: 548:Euler's line 512: 508: 504: 498: 496: 486:circumcircle 484: 480:circumcenter 478: 468: 466: 453:circumcenter 426: 299: 289: 282: 279: 262:trigonometry 259: 255:circular-arc 237: 231: 205: 199:determine a 178: 167: 161: 155: 148:plane figure 125: 112: 96: 94: 36: 6953:Star-shaped 6928:Rectilinear 6898:Equilateral 6893:Equiangular 6857:Hendecagram 6701:11–20 sides 6682:Octagon (8) 6672:Hexagon (6) 6647:Monogon (1) 6489:Equilateral 6071:: 119–120. 6032:Lang, Serge 5866:486-60088-2 5457:: 161–165. 5440:Works cited 5392:Berger 2002 5093:(1): 15–24. 5003:Kalman 2008 4989:46–47 4929:Gonick 2024 4880:Gonick 2024 4809:Gonick 2024 4797:Gonick 2024 4785:Gonick 2024 4773:Gonick 2024 4761:Gonick 2024 4695:Gonick 2024 4667:Gonick 2024 4308:, p. 4 3924:convex hull 3838:cusp points 1271:and height 1043:Some basic 1028:hatch marks 597:orthocenter 514:orthocenter 457:orthocenter 304:right angle 240:curvilinear 201:tetrahedron 119:dimensional 117:, are zero- 6958:Tangential 6862:Dodecagram 6640:1–10 sides 6631:By number 6612:Tangential 6592:Right kite 6408:"Triangle" 6195:: 113–115. 5330:, p.  5311:, p.  5295:, p.  5279:, p.  5256:, p.  4987:, p.  4915:, p.  4901:Smith 2000 4865:Heath 1926 4823:, p.  4725:, p.  4723:Axler 2012 4709:, p.  4707:Young 2017 4681:, p.  4655:Heath 1926 4641:, p.  4639:Holme 2010 4625:, p.  4542:, p.  4523:, p.  4507:, p.  4491:, p.  4473:, p.  4464:, p.  4445:, p.  4429:, p.  4413:, p.  4397:, p.  4381:, p.  4379:Holme 2010 4365:, p.  4363:Holme 2010 4351:Heath 1926 4335:, p.  4326:, p.  4299:, p.  4278:Stahl 2003 4262:Heath 1926 4246:, p.  4237:, p.  4217:Heath 1926 4210:, p.  4193:Byrne 2013 4179:, p.  4117:References 3657:with area 2495:Inequality 1546:. Letting 434:concurrent 412:Properties 18:Triangular 6984:Triangles 6938:Reinhardt 6847:Enneagram 6837:Heptagram 6827:Pentagram 6794:65537-gon 6652:Digon (2) 6622:Trapezoid 6587:Rectangle 6537:Bicentric 6499:Isosceles 6476:Triangles 6418:EMS Press 6278:. Wiley. 5917:CiteSeerX 5778:CRC Press 5665:(2013) . 5504:. Wiley. 5377:19 August 5355:19 August 5254:Hann 2014 5065:0025-5572 4821:Ryan 2008 4623:Ryan 2008 4540:King 2021 4521:Ryan 2008 4505:Ryan 2008 4489:King 2021 4471:King 2021 4443:Ryan 2008 4333:Ryan 2008 4297:Ryan 2008 4244:Ryan 2008 4165:Footnotes 4135:triangle. 4033:× 4028:∘ 3907:− 3878:− 3118:¯ 3105:⋅ 3100:¯ 3083:¯ 3070:⋅ 3065:¯ 3041:¯ 3028:⋅ 3023:¯ 3006:¯ 2993:⋅ 2988:¯ 2964:¯ 2951:⋅ 2946:¯ 2929:¯ 2916:⋅ 2911:¯ 2782:γ 2776:β 2770:α 2652:− 2626:− 2470:⋅ 2413:− 2367:− 2321:− 1740:(such as 1661:− 1646:− 1631:− 1462:γ 1459:⁡ 1407:γ 1401:⁡ 1367:γ 1071:congruent 993:γ 987:⁡ 978:β 972:⁡ 963:α 957:⁡ 945:γ 942:⁡ 926:β 923:⁡ 907:α 904:⁡ 871:γ 851:β 831:α 811:γ 791:β 771:α 761:collinear 678:symmedian 606:excircles 581:excircles 438:collinear 233:geodesics 212:curvature 88:see below 6978:Category 6913:Isotoxal 6908:Isogonal 6852:Decagram 6842:Octagram 6832:Hexagram 6633:of sides 6562:Harmonic 6463:Polygons 6377:(2017). 5880:Springer 5841:(1926). 5798:(2024). 5722:(1967). 5570:(1995). 5500:(1997). 5172:40378417 4109:and the 4063:, where 3205:distinct 2890:, then: 2546:hexagons 2514:Rigidity 1731:Elements 1602:be the 1045:theorems 748:and the 668:centroid 663:midpoint 661:and the 642:centroid 576:inradius 571:incircle 565:incenter 500:altitude 475:midpoint 461:incircle 284:Elements 243:triangle 114:vertices 109:geometry 97:triangle 61:vertices 42:Triangle 6933:Regular 6878:Concave 6871:Classes 6779:257-gon 6602:Rhombus 6542:Crossed 6204:College 6178:3618298 6116:0367792 6108:2319703 5947:1299166 5939:2974536 5708:1168956 5590:1377265 4607:2430410 4103:Fractal 2487:is the 1892:⁠ 1846:⁠ 1842:⁠ 1796:⁠ 1792:⁠ 1746:⁠ 1422:⁠ 1381:⁠ 1357:⁠ 1337:⁠ 1333:⁠ 1313:⁠ 1293:⁠ 1273:⁠ 1269:⁠ 1249:⁠ 1199:⁠ 1179:⁠ 1175:⁠ 1155:⁠ 1151:⁠ 1131:⁠ 1100:AAcorrS 1037:similar 883:exists 440:; here 228:surface 101:polygon 6943:Simple 6888:Cyclic 6883:Convex 6607:Square 6547:Cyclic 6509:Obtuse 6504:Kepler 6387:  6354:  6323:  6301:  6282:  6263:  6238:  6211:  6176:  6143:  6114:  6106:  6050:  6020:  5968:  5945:  5937:  5919:  5894:  5864:  5827:  5806:  5784:  5759:  5734:  5706:  5675:  5651:  5632:  5613:  5588:  5578:  5533:  5508:  5486:  5426:  5170:  5063:  4605:  4566:  4155:convex 4005:sphere 3653:Every 2756:, etc. 2550:nature 2457:where 1736:Given 863:, and 803:, and 691:Angles 658:vertex 652:median 320:Euclid 247:curved 172:. The 169:height 122:points 105:shapes 6918:Magic 6514:Right 6494:Ideal 6484:Acute 6174:JSTOR 6104:JSTOR 5935:JSTOR 5168:JSTOR 5083:(PDF) 4282:p. 37 4122:Notes 3815:disks 3769:conic 3638:is a 2593:with 306:is a 253:with 236:). A 193:plane 127:edges 99:is a 57:Edges 6948:Skew 6572:Kite 6467:List 6385:ISBN 6369:(6). 6352:ISBN 6321:ISBN 6299:ISBN 6280:ISBN 6261:ISBN 6236:ISBN 6209:ISBN 6141:ISBN 6048:ISBN 6018:ISBN 5966:ISBN 5892:ISBN 5825:ISBN 5804:ISBN 5782:ISBN 5757:ISBN 5732:ISBN 5673:ISBN 5649:ISBN 5630:ISBN 5611:ISBN 5576:ISBN 5531:ISBN 5506:ISBN 5484:ISBN 5424:ISBN 5379:2024 5357:2024 5061:ISSN 4564:ISBN 3987:and 3970:and 3938:and 3763:The 3744:The 3634:The 3191:The 3170:and 3166:The 2870:and 2505:The 1335:and 1127:area 1107:Area 703:The 509:foot 505:base 451:The 222:. 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Index

Triangular
Triangle (disambiguation)

Edges
vertices
Schläfli symbol
Area
see below
polygon
shapes
geometry
vertices
dimensional
points
edges
line segments
internal angles
sum of angles of a triangle
straight angle
plane figure
planar region
base
apex
height
area of a triangle
Euclidean geometry
straight line
all lie on the same straight line
plane
three-dimensional Euclidean space

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