## The Lesson

An equilateral triangle is a triangle that has three equal angles and three sides the same length.**Note:**The lines through the sides of the triangle in the image above indicate they are of equal length. The arcs indicate the angles are equal.

## Dictionary Definition

The Merriam-Webster dictionary defines an equilateral triangle as "a triangle in which all three sides are the same length."## Real Examples of Equilateral Triangles

Below are real examples of equilateral triangles.In each case

- All 3 sides are the same length.
- All 3 angles are the same (60°).

## Properties of Equilateral Triangles

## The Interior Angles of an Equilateral Triangle

Each interior angle of an equilateral triangle is 60°.## The Symmetry of Equilateral Triangles

An equilateral triangle has 3 lines of symmetry.## What's in a Name?

'Equilateral' comes from the Latin word "aequilateralis". 'aequi' comes from the word "aequalis", meaning 'equal', and 'lateralis' means 'relating to the side'. 'Equilateral' means 'equal sides'.## The Interior Angles of an Equilateral Triangle

The interior angles of any triangle add up to 180°. Since all three angles are the same in an equilateral triangle, the 180° is divided equally between each interior angle.This is why each angle is 60°.

## Interactive Game on the Types of Triangle

**the types of triangle**.