Question

A certain coin is a circle with diameter 18 mm. What is the exact area of either face of the coin?
The exact area of either face of the coin is mm2.
(Simplify your answer. Type an exact answer in terms of st.)

Answer 1

Answer:    81pi

============================================================

Explanation:

If the diameter is d = 18, then the radius is half that at r = d/2 = 18/2 = 9

Then that radius is plugged into the circle area formula below

A = pi*r^2

A = pi*9^2

A = pi*81

A = 81pi

If you were to use an approximation like pi = 3.14, then the approximate area would be 81*pi = 81*3.14 = 254.34 mm^2; however, your teacher wants you to write the exact area.