SOLUTION: What is the circumference of a circle if the area is {{{81pi}}}?

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Question 319932: What is the circumference of a circle if the area is 81pi?
Found 2 solutions by Edwin McCravy, stanbon:
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
What is the circumference of a circle if the area is 81pi?

Use the Area formula A=pi%2Ar%5E2 to find the radius; then use that
value for r in the circumference formula C=2pi%2Ar. 

A+=+pi%2Ar%5E2
81pi=pi%2Ar%5E2
%2881pi%29%2Fpi=pi%2Ar%5E2%2Fpi

%2881cross%28pi%29%29%2Fcross%28pi%29=cross%28pi%29%2Ar%5E2%2Fcross%28pi%29

81=r%5E2
sqrt%2881%29=sqrt%28r%5E2%29
9=r

C+=+2pi%2Ar
C+=+2pi%2A9
C=18pi

Edwin

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
What is the circumference of a circle if the area is 81pi
-----------
Area = pi*r^2
---
Solve for "r":
pi*r^2 = 81pi
r^2 = 81
r = 9
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Circumference = 2*pi*r
C = 2*pi*9
C = 18*pi
================
Cheers,
Stan H.