Posted by **Anonymous** on Thursday, January 24, 2008 at 9:36pm.

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.

- Calculus -
**Reiny**, Thursday, January 24, 2008 at 10:25pm
dV/dr = 8pir*dr/dr

which at r = 6 is 8pi(6)

=48pi

- Calculus (for reiny) -
**Anonymous**, Thursday, January 24, 2008 at 11:04pm
actually the answer is 64pi ft^3/ft.

can you figure out what you did wrong? thanks.

- Calculus (for reiny) -
**Reiny**, Thursday, January 24, 2008 at 11:18pm
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.

Check your typing

- Calculus -
**Anonymous**, Thursday, January 24, 2008 at 11:44pm
sorry. yes, r should be equal to 8. Thanks.

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