SOLUTION: The total area of a right circular cylinder is 42 pi. If the height of the cylinder is 4, find the length of the radius.

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Question 537986: The total area of a right circular cylinder is 42 pi. If the height of the cylinder is 4, find the length of the radius.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
The total area of a right circular cylinder is 42 pi.
If the height of the cylinder is 4, find the length of the radius.
:
2(pi%2Ar%5E2) + 2%2Api%2Ar%2A4 = 42%2Api
divide by 2%2Api, results:
r^2 + 4r = 21
A quadratic equation
r^2 + 4r - 21 = 0
Factors to
(r+7)(r-3) = 0
the positive solution is all we want here
r = 3 is the radius