How Are The Angles Of An Equilateral Triangle Related, Angles In Equilateral Triangles

The Lesson

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

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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.


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