Q. 344.5( 4 Votes )

# The circumference of a circle whose area is 81πr^{2}, is

A. 9πr

B. 18πr

C. 3πr

D. 81πr

Answer :

Let the radius of the circle be R

Area of circle = πR^{2}

81 πr^{2} = πR^{2}

R = r

R = 9r

Circumference = 2 πr

⇒ 2πR

⇒ 2 π(9r)

⇒ 18 πr

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