How to calculate the area of circle giving your answer in terms of Pi.

In this hub I will show you how to find the area of circle giving your answer in terms of Pi (π).

First of all you need to remember the formula for calculating the area of a circle:

A = πr²

A stands for area, π stands for Pi and r is the radius of the circle (the distance halfway across).

Example 1

Work out the area of circle that has a radius of 7m, giving your answer in terms of Pi.

All you need to do is substitute r = 7 into A = πr²

A = πr²

= π × 7²

Since 7² = 49 (since 7 × 7 = 49) then you have:

= π × 49.

= 49π

So the final answer is 49π m² (put the number before Pi)

Example 2

Work out the area of circle that has a diameter of 22cm, giving your answer in terms of Pi.

This time the diameter is given (the distance all the way across) so you need to halve this to give the radius. Therefore, plug in r = 11 into A = πr²

A = πr²

= π × 11²

Since 11² = 121 (since 11 × 11 = 121) then you have:

= π × 121.

= 121π

So the final answer is 121π cm² (put the number before Pi)

Example 3

Work out the area of this circular lawn giving your answer in terms of Pi.

The radius of this lawn is 13m so you need to put this value into the formula.

A = πr²

= π × 13²

Since 13² = 169 (since 13 × 13 = 169) then you have:

= π × 169.

= 169π

So the final answer is 169π m² (put the number before Pi)

For some help on working out the area of a semicircle click here.

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3 comments

klordy 3 years ago

thx it really helped my son with hmework


A.A. Zavala profile image

A.A. Zavala 5 years ago from Texas

Very informative. Thank you for sharing.


Husky1970 5 years ago

If you have a certain linear quantity of boundary and want to enclose the greatest area possible with it, what should you do? Say you have 100 feet of fence and want to enclose the greatest area possible.

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