Question

If the area of a circle is 81 π square feet, find its circumference. ​

Answer 1

Answer:

Circumference= 18π feet

Step-by-step explanation:

area of circle = πr²

Given area = 81π sq. feet

∴ πr² = 81π

r²=81

r=√81 = ±9

Radius can't be negative. So, r=9 feet.

Circumference = 2πr

=2π*9

=18π feet.

Answer 2

Given :

• Area if circle = 81π feet²

To Find :

• Circumference of circle = ?

Solution :

As, we are given area of circle = 81π feet²

We know that :

• Area of circle = πr²

=> πr² = 81π feet²

=> r² = 81 feet²

=> r² = (9 feet)²

=> r = 9 feet

Hence, radius of circle = 9 feet.

Now, we have to find circumference of circle,

we know that :

• Circumference of circle = 2πr

=> Circumference = 2 × 22/7 × 9

=> Circumference = 396/7

=> Circumference = 56.57 feet (approx.)

Hence, circumference of circle is approximately 56.57 feet.