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Revise Similar Triangles

In this worksheet, students will revise similar triangles and use proportions to work out the lengths of sides.

'Revise Similar Triangles' worksheet

Key stage:  KS 3

Year:  Year 9 Maths worksheets

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Solve Problems Involving Perimeters and Areas of 2D Shapes

Popular topics:   Geometry worksheets

Difficulty level:  

Worksheet Overview

Triangles that have exactly the same angles are similar.


If two angles match, the third angle will automatically match as the angle sum is always 180º.


Similar triangles have corresponding sides which are in the same ratio or proportion.


similar triangles


Here, the lengths of the sides in the right-hand triangle are 1.5 times the lengths of the matching sides in the left-hand triangle.



Find the value of x from the information given in these triangles.


similar triangles



The triangles are similar because two angles match, and so will the third too.

Comparing corresponding sides, we get that the scale factor is 7 ÷ 5 = 1.4


x = 1.4 × 6 = 8.4 cm


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