SOLUTION: What is the area of a circle with circumference 18pi centimeters? Give your answer in terms of pi. Show work Thanks

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Question 161609: What is the area of a circle with circumference 18pi centimeters? Give your answer in terms of pi. Show work
Thanks
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Circumference of any circle is:
C = (pi)/d
where
C is circumference
d is diameter
.
Area of any circle:
A = (pi)r^2
where
A is area
r is radius
.
Of course, radius is half the diameter or
r = d/2
.
Pulling it all together:
Since they gave you circumference, use the circumference formula to find d (diameter):
C = (pi)/d
18(pi) = (pi)/d
18=d
.
Extract radius (r):
r = d/2
r = 18/2
r = 9 cm
.
plug it into the formula for area of a circle:
A = (pi)r^2
A = (pi)9^2
A = 81(pi) square cm (this is what they're looking for)