Isosceles Triangle

Lesson Objective

In this lesson, we will learn about isosceles triangles...

Study Tips

Tip #1

When a triangle has two sides (edges) of equal length, this triangle can be called an isosceles triangle. See some examples below:

Tip #2

Since this type of triangle has two sides of equal length, the base angles will definitely be the same. See some examples below:

The base angles of an isosceles triangle are the same

The math video below will explain more...

Math Video

Lesson Video

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Math Video Transcript

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In this lesson, we will learn about isosceles triangle.

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A triangle is an isos. triangle, when it has two sides of equal length.

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Now, to demonstrate this, let's move vertex C to the right.

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When these 2 sides have the same length, we get an isos. triangle.

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Here, the side BC will be the base of this triangle.

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Note that, since these 2 sides have the same length, these two base angles will also be the same.

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Let's move vertex C and vertex B.

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Notice that, we have another isos. triangle.

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Now, there is a right angle. Therefore, this triangle can be called right isos. triangle.

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Let's see some examples.

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Is this an isos. triangle?

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Since this triangle has 2 sides of equal length, this is an isos. triangle.

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Next example, how about this triangle?

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Notice that, these two angles are the same. Hence, these 2 sides must have the same length.

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Hence, this is an isos. triangle.

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Last example. Now, all the sides of this triangle do not have the same length.

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Therefore, this is not an isos. triangle.

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That is all for this lesson.

Practice Questions & More

Multiple Choice Questions (MCQ)

Now, let's try some MCQ questions to understand this lesson better.

You can start by going through the series of questions on isosceles triangles or pick your choice of question below.

Question 1

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