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Explanation:
The area 81pi square meters leads to the radius 9 meters
Use the formula A = pi*r^2 to see why this is the case. You plug in A = 81pi and solve for r to get r = 9.
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Once you know the radius, you can determine the circumference C
C = 2*pi*r
C = 2*pi*9
C = 2*9*pi
C = 18pi
The circumference is the perimeter, or distance, around the circle.
