Ok, so I have a general question about integrals that I hope someone can help me understand through a specific question. One of the problems that I am working on is to evaluate the following integral:

$\displaystyle \frac{q}{2a} \cdot \int_{-a}^a \frac{dx}{(r^2-2rx+a^2)^{1/2}}$

where q>0.

The problem asks me to evalaute the integral for two cases: (1) when 0 is less than or equal to r is less than or equal to a and (2) when r > a. I just get that the integral's solution is q/r. How will the relative sizes of r and a be important? Thanks!