Lots of calculus buried in that equation, Salmo. The derivative of the volume of a sphere is surface area of a sphere (multiply equation by the integer value of the exponent and drop the exponent value by 1).

Volume sphere=4/3(3.14)r^3, becomes Area sphere=4(3.14)r^2

Just like the circumference of a circle is derived from a circle's area.

Circle area=(3.14)r^2, becomes Circumference circle=2(3.14)r

The integrals that relate the two dimensional circle circumference and area to the three dimensional equations above are somewhat complicated to describe here, but they involve an analysis called solids of revolution, or the shell method. You can Google these derivations easy enough if you want to see the math. :-)