How about backing off the not-understanding bit, you donkey! Perhaps I don't articulate the theory to your liking, but I understand perfectly. Analytically, the area of a two dimentional surface or the volume of a solid approches it's true value as the sample thickness of the variable approches zero in integration.

I took Analitical Geometry Calculus, as well as Differential Equations and Linear Algebra. I loved studying math.