Question

why is the surface area of a cube not the derivative of a volume?

Answer 1

You have to start from the origin. Try calculating it in terms of r, where x=2r. You will get the right answer

Answer 2

Nevermind, I lied.

Answer 3

Ok, I was half right.

The formula works for cubes and squares if you think of the area of a square being 4r^2, and the volume of cube being 8r^3, where r is the radius and x=2r