Calculate the Third Angle in a Triangle

In this worksheet, students will calculate the third angle in a triangle.

Key stage:  KS 2

Curriculum topic:   Geometry: Properties of Shapes

Curriculum subtopic:   Identify Angles at a Point

Popular topics:   Angles worksheets, Geometry worksheets

Difficulty level:

Worksheet Overview

In this activity, we will learn how to identify the missing angle in a triangle.

Remember: The angles in any triangle add up to a total of 180°

Let's try an example question together.

Example

Here is a scalene triangle.

All of its angles and sides are different.

What is the size of the angle marked with a question mark?

Here, we have been given two of the angles: 54° and 64°

To find the missing angle we need to add these two angles and subtract the total from 180.

54 + 64 = 118

180 - 118 = 62

The missing angle is 62°

We can check this is correct by doing: 54 + 64 + 62 = 180

Let's have a go at some questions now.

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