The circumference of a circle is 18π in. What is the area, in square inches? Express your answer in terms of piπ.
The circumference of a circle is given by the formula C = 2πr, where C is the circumference and r is the radius of the circle.
In this case, we are given that the circumference is 18π inches.
Plugging this into the formula, we get 18π = 2πr.
Simplifying, we divide both sides by 2π to solve for r:
r = 9 inches.
The area of a circle is given by the formula A = πr^2, where A is the area and r is the radius of the circle.
Plugging in the value of the radius we found, we get:
A = π(9)^2 = 81π square inches.
So, the area of the circle is 81π square inches.