Triangle::sides    Angles::angle    Length::right    Three::triangle    Vertices::lengths    Which::other

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{{#invoke:Infobox|infobox}} 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 <math>\triangle ABC</math>.

In Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane (i.e. a two-dimensional Euclidean space). This article is about triangles in Euclidean geometry except where otherwise noted.

Types of triangle

Euler diagram of types of triangles, using the definition that isosceles triangles have at least 2 equal sides, i.e. equilateral triangles are isosceles.

Triangle sections
Intro  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  Figures circumscribed about a triangle  Specifying the location of a point in a triangle  Non-planar triangles  Triangles in construction  See also  Notes  References  External links  

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