The formula for the area of a circle is A = πr^2, where A is the area and r is the radius.
Given that the area of the circle is 81π cm^2, we can set up the equation:
81π = πr^2
Dividing both sides by π, we get:
81 = r^2
Taking the square root of both sides, we get:
r = 9
Therefore, the radius of the circle is 9 cm.