# Find Missing Angles in Special Triangles

In this worksheet, students will find missing angles in special triangles.

Key stage:  KS 3

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Apply Facts About Angles and Sides

Difficulty level:

#### Worksheet Overview

In this activity, we are going to be looking at angles in special triangles!

We know that:-

We can use it to find missing angles in triangles!

We know that the sum of the three angles is 180o

We can say that R = 180 - (25 + 96)

R = 180 - 121

R = 59o

There are two special triangles for us to consider.

1) The Equilateral Triangle

All the sides are the same length.

All the angles are the same.

2) Isosceles Triangle

Two of the sides are the same length.

Two of the angles are the same

These facts help us to find missing angles in triangles.

Let's have a look at a question.

Example

Calculate the size of angle A in the equilateral triangle below.

As the triangle is equilateral, we know that all the angles are the same.

We also know that angles in a triangle add up to 180o

Therefore, angle A = 180 ÷ 3 = 60o

Let's try some mixed questions now!

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