If the area of a circle is 81pi square feet, find its circumference.
Choices:
A) 15 B) 16 C) 17 D) 18 E) 19
The area is given by pi * r *r. Hence   pi* r *r = 81 pi   r * r = 81 * hence r = 81 feet   The circumference is given by   2 * pi * r = 2 * pi *9 = 18 pi feet   correct answer 18
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If the area of a circle is 81pi square feet, find its circumference.