College Math Teaching

July 31, 2014

Stupid question: why does it appear to us that differentiation is easier than anti-differentiation?

Filed under: calculus, elliptic curves, integrals — Tags: , — collegemathteaching @ 8:05 pm

This post is inspired by my rereading a favorite book of mine: Underwood Dudley’s Mathematical Cranks

There was the chapter about the circumference of an ellipse. Now, given $\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$ it isn’t hard to see that $s^2 = {dx}^2 + {dy}^2$ and so going with the portion in the first quadrant: one can derive that the circumference is given by the elliptic integral of the second kind, which is one of those integrals that can NOT be solved in “closed form” by anti-differentiation of elementary functions.

There are lots of integrals like this; e. g. $\int e^{x^2} dx$ is a very famous example. Here is a good, accessible paper on the subject of non-elementary integrals (by Marchisotto and Zakeri).

So this gets me thinking: why is anti-differentiation so much harder than taking the derivative? Is this because of the functions that we’ve chosen to represent the “elementary anti-derivatives”?

I know; this is not a well formulated question; but it has always bugged me. Oh yes, I am teaching two sections of first semester calculus this upcoming semester.