SOLUTION: What is the length of the diameter of a circle with an area of 9pi square units?

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Question 894054: What is the length of the diameter of a circle with an area of 9pi square units?
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
A=pi%2Ar%5E2
A is for area
r is for radius
d is for diameter
d=2r, according to definition of diameter.

You are given A and you want to find d.

pi%2Ar%5E2=A
pi%2A%28d%2F2%29%5E2=A
%28d%2F2%29%5E2=A%2Fpi
d%2F2=sqrt%28A%2Fpi%29
highlight%28d=2%2Asqrt%28A%2Fpi%29%29

Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!

What is the length of the diameter of a circle with an area of 9pi square units?


pi+%2A+r%5E2+=+area_of_circle

Let diameter be D

Since area = 9%28pi%29, and radius = D%2F2, then: pi+%2A+r%5E2+=+area_of_circle becomes: pi+%2A+%28D%2F2%29%5E2+=+9+%2A+pi

pi+%2A+%28D%5E2%2F4%29+=+9+%2A+pi

%28pi+%2A+D%5E2%29%2F4+=+9+%2A+pi

pi+%2A+D%5E2+=+36+%2A+pi ------ Cross-multiplying

pi%2A%28D%5E2%29+=+pi+%2A+%2836%29 ------  Factoring out GCF, pi 

D%5E2+=+36

D, or diameter = sqrt%2836%29, or highlight_green%286%29