# Math Help - application of differentiation question

1. ## application of differentiation question

Hey

I am having trouble with this question.

Consider a cylindrical can which has some fixed volume V. If r is the radius of the circular cross-section and h is the height, show that the values of r and h which will minimise the surface area are related by h = 2r.

Now I have Surface Area (SA) = $2\pi r^2 + 2 \pi rh$

Then i replace the h in that equation with h in terms of r.

$SA = 2\pi r^2 + 2 \pi r * V/ (\pi r^2)$

But then how do I get rid of the V?

2. $V$ is a constant...