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Radius of Circles From Their Area

In this worksheet, students calculate the radius of a circle given its area.

'Radius of Circles From Their Area' worksheet

Key stage:  KS 3

Curriculum topic:   Geometry and Measures

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

Difficulty level:  

Worksheet Overview

The formula for the area of a circle, A, in terms of its radius, r, is:

  A = πr2

 

We can rearrange this formula to make r the subject.

The formula for the radius of a circle, r, in terms of its area, A, is:

 

Example

Calculate the radius, r cm, of a circle which has an area of 100 cm2

Give your answer to 3 sig. figs.

 

Answer

r2 = 100 ÷ π = 31.831

r = √31.831 = 5.641896 ≈ 5.64 cm (3 s.f.)

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