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 Question from india, a student: How do you find the radius of a circle if only the area is given to you?

Hi,

I am going to answer a similar question.

How do you find the radius of a circle if only the perimeter is given to you?

The key here is to know an expression that links the perimeter and radius of a circle. If $P$ is the perimeter of a circle of radius $r$ then

$P = 2 \pi \; r.$

Solving this equation for $r$ yields

$r = \frac{P}{2 \pi}.$

Thus if you know the perimeter you can calculate the radius.

Now try to see how you can calculate the radius of a circle if you know the area.

Penny

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