# Calculus

The function V=4pir^2 describes the volume of a right circular cylinder of heigh 4ft and radius r feet. Find the (instantaneous) rate of change of the volume with respect to the radius when r=6. Leave the answer in terms of pi.

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1. dV/dr = 8pir*dr/dr
which at r = 6 is 8pi(6)
=48pi

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posted by Reiny
2. actually the answer is 64pi ft^3/ft.
can you figure out what you did wrong? thanks.

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posted by Anonymous
3. Nope, for the data you gave me the answer is 48pi

this is a very straighforward question,
to have an answer of 64 pi, perhaps you were to find the rate when r = 8.

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posted by Reiny
4. sorry. yes, r should be equal to 8. Thanks.

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posted by Anonymous

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