I am working on an optimization problem right now and ran into the following situation.

$\displaystyle V = piR^2H = 8$

$\displaystyle H = 8/piR^2$

$\displaystyle H = 2srt(2)/piR$

$\displaystyle A = H2piR+piR^2$

$\displaystyle A = (2rt(2)/piR)2piR+piR^2$

$\displaystyle A = 4srt(2)+piR^2$

$\displaystyle dA/dR = 2piR$

I think I have done this wrong, but I am fairly tired right now and can't seem to find my mistake.