# The area of a circle with radius r given by the formula A = pi r^2. If a circle has area 81 pi square in inches, what is the radius?

## To find the radius of a circle given its area, you can rearrange the formula for the area of a circle and solve for the radius.

Given that the area of the circle is 81 pi square inches and the formula for the area of a circle is A = pi r^2.

Step 1: Substitute the given area into the formula.
81 pi square inches = pi r^2

Step 2: Divide both sides of the equation by pi to isolate r^2.
81 square inches = r^2

Step 3: Take the square root of both sides of the equation to solve for r.
√81 square inches = √r^2

Step 4: Simplify the equation.
9 inches = r

Therefore, the radius of the circle is 9 inches.

## To find the radius of a circle given its area, you can use the formula A = πr^2, where A represents the area and r represents the radius.

In this case, we are given that the area of the circle is 81π square inches. So we can substitute this value into the formula:

81π = πr^2

Dividing both sides of the equation by π, we get:

81 = r^2

To find the radius, we need to take the square root of both sides of the equation to eliminate the squared term:

√81 = √r^2

Since the square root of 81 is 9, we have:

9 = r

Therefore, the radius of the circle is 9 inches.