Derivatives-volume of a cyclinder

[roman15]

Homework Statement

im just reviewing for a test tomorrow and im stuck on this question, any help is appreciated

if the volume of a cylinder is v=50-3pir^3, the surface area is 100cm^2 and the range of the radius is 0<r<3, what is the radius that will give the maximal volume?

Homework Equations

The Attempt at a Solution

 

[Mark44]

I don't think you're giving us all the information. Can we assume that this is a circular cylinder? And that formula for the volume is very unusual - it gives negative values for volume when r is greater than about 1.744 cm.

Are you sure you have given us the exact information of this problem?

 

[roman15]

im so sorry, i was using the wrong equation for the volume, is should be v=50r-pir^3, now the question is really easy but thanks for taking your time to help