Math Help: How to Calculate the Area of Circle and Get an 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).
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.
So the final answer is 49π m² (put the number before Pi)
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.
So the final answer is 121π cm² (put the number before Pi)
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.
So the final answer is 169π m² (put the number before Pi)
Questions & Answers
What is the area of a circle whose diameter is 10cm?
First half the diameter (10) to give the radius, so 10 divided by 2 is 5.
Now square the radius which is 25 (5^2)
Now multiply 25 by Pi to give 25Pi.
If you want your answer as a decimal then multiply 25 by 3.14 to give 78.5 to 1 decimal place.
Can you work out the perimeter of a semicircle with a radius of 4?
First double the radius to give 8, now multiply this by Pi to give 8Pi. Now half 8Pi to give 4Pi.
So the length of the arc is 4Pi.
Now add on the diameter to give a final answer of 4Pi + 8.Helpful 1
Find the area of a circle with a radius of 15cm? Give your answer in terms of pi?
Square the radius and multiply by Pi. 15^2 is 225, so the answer is 225Pi. Just leave the pi are the end of the number.Helpful 2
Can you work out the perimeter of a semicircle with a radius of 3cm? Give your answer in terms of pi?
To work out the cirumference multiply the diameter by pi.
The diameter is 6, and so 6 multiplied by Pi is 6Pi.
You can leave the answer as 6Pi and the question is asking for an exact answer and not a decimal answer.Helpful 15
The circumference of a circle is 18π inches, so what is the area in terms with π?
Divide the 18π by π to give the diameter of the circle which gives 18.
Half 18 to give a radius of 9.
Now use πr^2 to give the area which comes to 81π .Helpful 11