Hi,

Im doing a differentiation problem and somewhere i am going wrong so I am just going to type out my work and see if anyone can help

Surface are of cylinder is 60cm and we need to find the maximum and minimum volume

2pi r(h+r)=60

h+r= 60/2pi r

h+r=30/ pi r

h= (30/pi r) -r

h= (30-pi r^2)/ pi r)

placing h into volume formula

v= pi r^2*h

substituting h leaves -pi r^3+30r

dr/dv= -3r^2+30r=0

3r(-r+10)

r=10

where do i go from here.

how do i find the maximum and minimum??