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For other meanings, such as the musical instrument that is also called a "triangle", see triangle (disambiguation).

A triangle is a shape or area, or a specific part of two dimension space. It has three straight sides and three points. The three angles of a triangle always add up to 180 degrees. It is the polygon with the least possible number of sides.

Types of triangles

A right triangle that is also isosceles

Triangles can be grouped according to how long their sides are

  • In an equilateral triangle all three sides have the same length
  • In an isosceles triangle two sides have the same length
  • In a scalene triangle all sides have different lengths

Triangles can also be grouped by their angles.


Triangles are extremely useful, because the ratio of the length of sides to an angle is always the same. Measuring objects using triangles is called Trigonometry. Some people have spent their entire lives studying triangles for use in trigonometry.

Modern computers usually use triangles to make more complex graphic images or shapes.

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