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
Outer Inscribed Squares Triangle -- from Wolfram MathWorld
Schematic plot of banana trees (adapted from Wolfram MathWorld
How to Calculate the Sides and Angles of Triangles Using
Schoute Center -- from Wolfram MathWorld
Circumtangential Triangle -- from Wolfram MathWorld
Heptagonal Triangle -- from Wolfram MathWorld
Seidel-Entringer-Arnold Triangle -- from Wolfram MathWorld
Third Morley Triangle -- from Wolfram MathWorld
D-Triangle -- from Wolfram MathWorld
Dual Tessellation -- from Wolfram MathWorld
My girlfriend had this thought about what an Apex is in a triangle
