A **triangle** is one of the basic shapes of geometry: a polygon with **three** corners or vertices and **three** sides or edges which are line segments. A triangle with vertices *A*, *B*, and *C* is denoted .

In Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane (i.e. a two-dimensional Euclidean space).

Read more about Triangle: Basic Facts, Existence of A Triangle, Points, Lines, and Circles Associated With A Triangle, Computing The Sides and Angles, Computing The Area of A Triangle, Further Formulas For General Euclidean Triangles, Morley's Trisector Theorem, Figures Inscribed in A Triangle, Partitioning Into Isosceles Triangles, Figures Circumscribed About A Triangle, Non-planar Triangles, Triangles in Construction