Question

Find the circumference of a circle whose area is 81πcm².

Answer 1

The Area of a Circle with radius r = πr²
Here, Area of a Circle = 81πcm²
⇒ 81π = πr²
⇒ 81 = r²
⇒ r = 9cm
The Circumference of a Circle with radius r = 2πr
The Circumference of a Circle with radius 9
= 2π x 9
= 18πcm.