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**nertil1** I was just wondering this. When you differentiate the volume of a sphere you find the surface area of a sphere. When you differentiate the area of a circle, you get the circumphrence of a circle. I have tried but I can't seem to apply this concept to cubes and squares. Like say for example the volume of a cube is x^3. When you differentiate that you get 3x^2, which isn't the surface area of the cube (at least I think so). also, if the area of a box was x^2, when you differentiate that you get 2x, is is not the perimeter of that box. Maybe I'm not applying the right idea here, but I was just wondering. What do you guys think