# Finding the Radius from the Area(KS3, Year 7)

## The Lesson

The radius of a circle is found from the area of a circle using the formula:

In this formula, A is the area of the circle. The image below shows what we mean by finding the radius from the area:

## How to Find the Radius from the Area

Finding the radius from the area is easy.

## Question

What is the radius of the circle, with area 10 cm2, below?

# 1

Radius = √ (Aπ)
Don't forget: √ means square root, / means ÷ and π is pi (≈ 3.14)

# 2

Substitute the area into the formula. In our example, A = 10.
Radius = √ (10π) Radius = √ (10 ÷ π) Radius = √ (10 ÷ 3.14) Radius = √ 3.18 Radius = 1.78 cm

The radius of the circle is 1.78 cm.

## Lesson Slides

The slider below shows another real example of how to find the radius of a circle from the area. Open the slider in a new tab

## Interactive Widget

Here is an interactive widget to help you learn about finding the radius of a circle from its area.
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