Triangle -- from Wolfram MathWorld

A triangle is a 3-sided polygon sometimes (but not very commonly) called the trigon. Every triangle has three sides and three angles, some of which may be the same. The sides of a triangle are given special names in the case of a right triangle, with the side opposite the right angle being termed the hypotenuse and the other two sides being known as the legs. All triangles are convex and bicentric. That portion of the plane enclosed by the triangle is called the triangle interior, while the

How to Calculate the Sides and Angles of Triangles Using

Penrose Tiles -- from Wolfram MathWorld

Taylor Center -- from Wolfram MathWorld

Steiner Triangle -- from Wolfram MathWorld

Inner Napoleon Triangle -- from Wolfram MathWorld

code golf - Draw A Reuleaux Triangle! - Code Golf Stack Exchange

Tangential Mid-Arc Triangle -- from Wolfram MathWorld

Triangle Function -- from Wolfram MathWorld

Mixtilinear Triangle -- from Wolfram MathWorld

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Heptagonal Triangle -- from Wolfram MathWorld

Inner Vecten Triangle -- from Wolfram MathWorld