For alternative meanings, see triangle (disambiguation).

A triangle is one of the basic shapes of geometry: a polygon with three vertices and three sides which are straight line segments.

Types of triangles

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Triangles can be classified according to the relative lengths of their sides:

• In an equilateral triangle all sides are of equal length. An equilateral triangle is also equiangular, i.e. all its internal angles are equal—namely, 60°; it is a regular polygonhttp://mathworld.wolfram.com/EquilateralTriangle.html
• In an isosceles triangle at least two sides are of equal length. An isosceles triangle also has two equal internal angles (namely, the angles where each of the equal sides meets the third side). An equilateral triangle is actually also an isosceles triangle, but not all isosceles triangles are equilateral triangleshttp://mathworld.wolfram.com/IsoscelesTriangle.html
• In a scalene triangle all sides have different lengths. The internal angles in a scalene triangle are all different.http://mathworld.wolfram.com/ScaleneTriangle.html

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