Proving smallest surface area of cylinder is when h=2r

[Kevin Sevcik]

Originally Posted by Manoel

Yes, but I was taking the partial derivative, so you just consider h a constant to take the derivative (that's far from a formal mathematical statement, but I don't know the exact English terms to make it more appropriate ).
I agree that the height and the radius are constrained by the fixed volume, but I don't see how that changes my solution.
It seems Sanddrag is taking Calculus A, or I, or 101, or whatever you call it in the USA. I didn't learn about partial derivatives until Calculus II.

The whole point of the problem is that h and r are varying, so you can't use a partial derivative and treat h as constant. At any rate, glad to hear you got it sanddrag. Looks like I forgot about setting A = 0 which makes it much easier to solve than I was thinking. oops.