# Find Missing Angles using Geometrical Rules

In this worksheet, students will apply their knowledge of geometrical rules to find missing angles.

Key stage:  KS 3

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Apply the Properties of Angles

Difficulty level:

#### Worksheet Overview

In this activity, we will be looking at angle problems involving all the rules we have learnt previously!

Let's recap what we know already!

Make a note of what you need here!

Angles around a point = 360o

Angles in a straight line = 180o

Angles in triangles = 180o

Angles in polygons = 180 x (number of sides - 2)

Vertically opposite (X) angles are equal

In parallel lines - (Z) alternate angles are equal

In parallel lines - (F) corresponding angles are equal

In parallel lines - (C) co-interior angles add up to 180o

Polygons - exterior angle = 360 ÷ number of sides

Polygons - interior angle = 180 - exterior angle

Typical geometry questions will have a mixture of these rules included!

Let's have a look at a typical question.

Example

Calculate the missing angle A.

Step 1 - Angles in a straight line with 126o

180 - 126 = 54o

Step 2 - The triangle is isosceles so both the base angles are the same

Step 3 - Angles in a triangle add up to 180o

We now have two angles so we can find the third one

A = 180 - (54 + 54)

A = 180 - 108

A = 72o

Let's have a go at some other questions now.

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