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.

## Answer this Question

## Related Questions

- calculus - the volume V of a right circular cone of height h=8 feet and radius r...
- calculus - What is the instantaneous slope of y =8/x at x = -3? What is the ...
- Calculus - Find the radius, volume, and hieght of the right- circlar cylindar ...
- CALCULUS help please - The radius of a right circular cylinder is given by t + 9...
- differential calculus - a right circular cylinder has a fixed height of 6 units...
- differential calculus - a right circular cylinder has a fixed height of 6 units...
- Calculus - t: 0 2 5 7 11 12 r'(t): 5.7 4.0 2.0 1.2 0.6 0.5 The volume of a ...
- Calculus - Let V be the volume of a right circular cone having height h and ...
- calculus - The radius of the base of a right circular cylinder is r com and the ...
- 4 CALCULUS study problem - 1. How fast does the radius of a spherical soap ...