I have read the tutorial of the calculus forum but still dont understand how you are supposed to prove that $\int_0^L \frac{a^2}{(x^2+a^2)^{3/2}} dx = \frac{L}{\sqrt{L^2+a^2}}$ (or rather $\int \frac{a^2}{(x^2+a^2)^{3/2}} dx = \frac{x}{\sqrt{x^2+a^2}}$). I have also looked on the internet and read my analysis-book, but I mostly find examples of rational integrals. What method should I employ? (I tried the substitution $u=\sqrt{x^2+a^2}$ without much success.)
Ok I found it now, I tried $x=a \tan \theta$ and it worked out. Sorry for bothering.