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# Differentiation Watch

1. Given that the volume (V cm^3) of an expanding sphere is related to its radius (r cm) by the formula v=4/3pir^3, find the rate of change of volume with respect to radius at the instant when the radius is 5 cm.

If

How is dv/dr equal to that?
2. It's just like anything else..multiply by the power and reduce it by 1.
3. (Original post by Zapdos)
It's just like anything else..multiply by the power and reduce it by 1.
I though so, I just wanted to make sure.

So 3r^2 but the 3 is divided by 3 to = 1 right?
4. (Original post by zed963)
I though so, I just wanted to make sure.

So 3r^2 but the 3 is divided by 3 to = 1 right?
3*(4/3) = 4
5. (Original post by zed963)
Given that the volume (V cm^3) of an expanding sphere is related to its radius (r cm) by the formula v=4/3pir^3, find the rate of change of volume with respect to radius at the instant when the radius is 5 cm.

If

How is dv/dr equal to that?
Differentiate both side with respect to r

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