Question

The area of a circle is 81pi in.squared. What is the circumference, in inches? Express your answer in terms of pi

Answer 1

18π

Explanation:

the area of a circle is :

A= r²*π where r is the radius

here r² =81⇒ r= 9

the circumference of a circle is :

P= 2*r*π

P= 18π

Answer 2

18 pi inches

Explanation:

The area of a circle is given by

A = pi r^2

81 pi = pi r^2

Divide by pi

81 = r^2

Take the square root of each side

sqrt(81) = sqrt (r^2)

9 = r

We want the circumference

C = 2 * pi * r

C = 2 * pi * 9

C = 18 pi