the triangle

Things & Objects
Free Picture Dictionary
All pictures can be used free of charge for personal, non-commercial use.
As a teacher you may also use them free of charge in your classroom.
Help us to create new images and to keep this free site running by making a donation – thank you!
make donation

Freely usable photos

Most pictures found here can be freely reused by students and teachers.

A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices A, B, and C is denoted .

In Euclidean geometry, any three points, when non-collinear, determine a unique triangle and simultaneously, a unique plane (i.e. a two-dimensional Euclidean space). In other words, there is only one plane that contains that triangle, and every triangle is contained in some plane. If the entire geometry is only the Euclidean plane, there is only one plane and all triangles are contained in it; however, in higher-dimensional Euclidean spaces, this is no longer true. This article is about triangles in Euclidean geometry, and in particular, the Euclidean plane, except where otherwise noted.