Question

What is the exact area of a circle with a diameter of 18 feet?

Answer 1

The formula for the area of a circle is 

$\pi r^{2}$

We know the diameter, and the radius is half of the diameter.  So the radius is 9.  Now we plug that into the formula.

$\pi 9^{2} =81 \pi$

So the answer is B, 81 pi square feet