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Use Algebra to Find the Angles in a Triangle

In this worksheet, students will form and solve equations by adding together the algebraic angles shown in each triangle.

'Use Algebra to Find the Angles in a Triangle' worksheet

Key stage:  KS 3

Year:  Year 9 Maths worksheets

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Interpret Mathematical Relationships Algebraically/Geometrically

Popular topics:   Geometry worksheets

Difficulty level:  

Worksheet Overview

The angles in a triangle add up to 180º.

This is no different when the angles are algebraic expressions.



Form an equation from the angles shown in this triangle and solve it to find the value of a.


algebra triangle



The sum of the angles = 180

a + 10 + a - 37 + a = 180


We simplify and solve this equation as follows:

3a - 27 = 180

3a = 207

a = 207 ÷ 3 = 69

a = 69º


From this we can then work out what each angle is:

The top angle is 69º

The angle below that is a + 10 = 69 + 10 = 79º

The final angle is a - 37 = 69 - 37 = 32º


Finally, add them altogether just to check that they do add up to 180: 

69 + 79 + 32 = 180º


Great work! Let's try some questions now.

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