Hi, 1. The problem statement, all variables and given/known data I was wondering whether any of you could kindly explain to me how the equation in the attachment was derived. I mean, how could I have known that it could be separated into these two fractions? 2. Relevant equations The attachment also specifies the integration to be performed in the rectangular region whose coordinates are given. 3. The attempt at a solution I know that the integrand, and integral, are zero for x=R, as R->infinity.