SOLUTION: What is the exact area of a circle with a diameter of 19 inches? (a) {{{9.5pi}}} square inches (b) {{{19pi}}} square inches (c) {{{38pi}}} square inch

Algebra ->  Surface-area -> SOLUTION: What is the exact area of a circle with a diameter of 19 inches? (a) {{{9.5pi}}} square inches (b) {{{19pi}}} square inches (c) {{{38pi}}} square inch      Log On


   

Question 311541: What is the exact area of a circle with a diameter of 19 inches?
(a) 9.5pi square inches
(b) 19pi square inches
(c) 38pi square inches
Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
What is the exact area of a circle with a diameter of 19 inches?
(a) 9.5pi square inches
(b) 19pi square inches
(c) 38pi square inches

The formula for the area of a circle is

A=pi%2Ar%5E2 where r represents the radius,

The radius is half the diameter.  Since the diameter is 19,
the radius is half that or 19%2F2

Substituting:

A=pi%2Ar%5E2
A=pi%2A%2819%2F2%29%5E2
A=pi%2A%28361%2F4%29
A=%28361pi%29%2F4 square inches, or as a decimal 90.25pi
So it isn't any of the choices you gave.  Maybe you mistyped and 
meant the circumference.  If so, then the formula for the
circumference is 

C=pi%2Ad
C=pi%2A19
C=19pi inches

So if you meant circumference then that is a choice; however
the unit for circumference is just plain 'inches', not 'square
inches'.  You'll have to ask your teacher what was meant, because
as it is the problem is botched.

Edwin