I think your question should read "A circle has an AREA of 81 PI square units...)
Circle Area = PI * radius^2
81 PI = PI * radius ^2
radius^2 = 81 PI / PI
radius^2 = 81
radius = 9
Therefore circle diameter = 9 * 2 = 18
Answer:
The circumference is 18.84 inches.
Step-by-step explanation:
To find the circumference of the circle we can use the formula:

Where C is circumference and r is radius.
Now that we have the formula, we can substitute the numbers:
