Isosceles Triangle Lesson for Kids

Instructor: Joy Blake

Joy has been a teacher for over ten years. She has primarily taught Middle School Math and has a Master's degree in Educational Leadership.

How do you think pizza and hangers relate to triangles? Read this lesson and you will find out what a triangle is. You also will learn about one type of triangle called an isosceles triangle.

Discovering Isosceles Triangles

Charles is moving into his college dorm room. He hangs up his clothes using coat hangers and decorates his room by putting up his college's school banner. He decides to take a break for a slice of pizza.

Throughout Charles's day he encountered a certain type of triangle called an isosceles triangle. The coat hangers, his school banner, and even the slice of pizza he ate are all examples of triangles. But more specifically they are examples of isosceles triangles.

What Makes a Triangle?

In order to know what an isosceles triangle is you first have to know how to talk about triangles.

If you look closely at the word 'triangle', you will see a word hidden inside it. That word is 'angle'. Angles are created when two lines meet or cross. The distance between the two lines is measured in units called degrees.

The 'tri' in triangle is a prefix that means three, so a triangle is a three-sided shape with three angles. Each time two of the sides meet, an angle is formed. When you add the measurement of all three angles of a triangle together, you'll always get 180 degrees.

Triangles are three-sided shapes with three angles.
A triangle

Now that you know what makes a triangle a triangle, let's figure out what's unique about an isosceles triangle.

What is an Isosceles Triangle?

Types of triangles are grouped by the length of their sides or measurements of their angles. An isosceles triangle has two sides that are the same length and one side that is a different length.

Because the slash marks are the same, we know that the two sides are equal in this triangle, making it isosceles.
An isosceles triangle with slash marks on the equal sides

When you measure the angles of an isosceles triangle, you will find that two of the angles have the same measurement. The angles opposite the equal sides will always be equal, too.

All three angles within an isosceles triangle are acute. Acute angles are less than 90 degrees.

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