How do you find the circumference and area of a circle with diameter of 18 inches?

1 Answer
Sep 29, 2015

Circumference = 18π (56.52 inches) and area = 81π (254.34 inches)

Explanation:

We use the following formulas: C=2πr and A=πr2, where C is circumference, A is area, and r is the radius (half the diameter).

First step is finding the radius. As I mentioned above, the radius is half the diameter, or in this case, half of 18. So, our radius is 9 inches. Now we can apply our formulas; we'll start with circumference:

C=2πr
C=2π9
C=18π, or approximately 56.52 inches (remember that π3.14)

For area:

A=πr2
A=π(9)2
A=81π, or approximately 254.34 inches