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Find the circumference of the circle whose area is 81π cm ^{2}.

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#### Solution

Area = π r^{2}

π r^{2} = 81 π

r^{2} = 81

r = 9 cm

circumference = 2 πr

= 2 × π × 9

= 18 π cm

araJmference - 18 π cm

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