## ::Triangle

### ::concepts

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 [itex]\triangle ABC[/itex].

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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