# What Is an Equilateral Triangle?

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."

# 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.

# 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°).
Geometry Lessons
##### Interactive Test
show

Here's a second test on equilateral triangles.
Here's a third test on equilateral triangles.

# 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°.

# Other Types of Triangle

Equilateral triangles are one type of triangle. There are also: