What is an equilateral triangle? Definition and examples

An equilateral triangle is a type of triangle that has all sides of equal length and all angles of equal measure.

Equilateral triangle

Some interesting properties of an equilateral triangle

  • An equilateral triangle has three lines of symmetry. Each line of symmetry starts from a vertex and is perpendicular to the side opposite the vertex
  • Since all sides of an equilateral triangle are equal, the perimeter is just three times the length of one of its sides
  • Since the sum of the angles in a triangle is equal to 180 degrees, each angle in an equilateral triangle measures 60 degrees
  • Each line of symmetry divides an equilateral triangle into two congruent triangles

Real-life examples of equilateral triangles

The Star of David made by two interlocking equilateral triangles is a good real-life example.

Star of David

The traffic sign below warning someone of a danger is an equilateral triangle

warning sign

The rack used to place billiard balls in their starting positions is shaped like an equilateral triangle

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