The circumference of a circle whose area is 81πr2, is

Let the radius of the circle be RArea of circle = πR281 πr2 = πR2R = rR = 9rCircumference = 2 πr⇒ 2πR⇒ 2 π(9r)⇒ 18 πr

Q34 of 131 Page 226

The circumference of a circle whose area is 81πr², is

Let the radius of the circle be R

Area of circle = πR²

81 πr² = πR²

R = r

R = 9r

Circumference = 2 πr

⇒ 2πR

⇒ 2 π(9r)

⇒ 18 πr

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