Solve Air Volume Increase for Spherical Balloon with Radius r

[DeltaBoy]

Hi guys, can you help me out with a homework question. I'm stuck and don't know what to do. Question state:

A spherical balloon with radius r inches has volume V(r) = (4/3)r3. Find a function that represents the amount of air A required to inflate the balloon from a radius of r inches to a radius of r + 1 inches.


Don't I just replace (r) with (r+1).. ?

The Attempt at a Solution

A(r)= (4/3)pi(r+1)^3 ??

Thanks a lot.

 

[genneth]

That would be the amount of air required to inflate a balloon of radius r+1. You want a *difference*.

 

[DeltaBoy]

ahh got it :) thank you genneth...