## The Lesson

An equilateral triangle is a triangle that has three equal angles and three sides the same length.

You are watching: How are the angles of an equilateral triangle related

**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 caseAll 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.

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## 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

**Here is an interactive game to help you learn about the types of triangle**.

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**Click on a triangle so it drops into the correct “bucket.”In total, there are 10 triangles to clear.If a triangle drops into the wrong “bucket,” you will lose one of your three lives.Good luck!**

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## The Test

Here are 3 randomly selected questions from a larger test that can be printed to create a handout or sent to students electronically.