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Find Missing Angles in a Triangle

In this worksheet, students will find missing angles in a triangle.

' Find Missing Angles in a Triangle' worksheet

Key stage:  KS 3

Year:  Year 7 Maths worksheets

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Derive/Use the Sum of Angles for Deduction

Difficulty level:  

Worksheet Overview

In this activity, we are going to be looking at angles in a triangle!




Let's take a triangle.

We can make one using a piece of A4 paper.


1) Cut the paper into a triangle - any type of triangle will do as long as the sides are straight!


2) Label the angles.


a triangle labelled a b and c


3) Tear off the corners like this!




4) Put the corners together like this!



It should form a half turn or straight line which is 180o

It works for any triangle - equilateral, isosceles, right-angled or scalene


Good to know! Make a note of this!



We can use it to find missing angles in triangles!


Let's try a typical question!


triangle with missing angle



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

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

R = 180 - 121

R = 59o


Let's try some questions now!

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