Theorems about triangles

In geometry, the angle bisector theorem is concerned with the relative lengths of the two segments that a triangle's side is divided into by a line that bisects the opposite angle. It equates their relative lengths to the relative lengths of the other two sides of the triangle.

Hinge theorem In geometry, the hinge theorem (sometimes called the open mouth…

Napoleon's theorem Napoleon's theorem: If the triangles centered on L, M, and…

Ceva's theorem For other uses, see Ceva (disambiguation). Ceva's theorem, case 1:…

Desargues's theorem Perspective triangles. Corresponding sides of the triangles, when extended, meet…

Stewart's theorem In geometry, Stewart's theorem yields a relation between the lengths…

Apollonius's theorem This article is about the lengths of the sides of…