Hey there, I'm working on a perturbation theory problem, and I have no clue where to start in solving an infinite series. It's an infinite square well with a delta function potential in the centre and I'm trying to find the 2nd order energy correction to Energy En. Anyway, what I've got is SIGMA [sin(m*Pi/2)sin(n*Pi/2)]^2/(n^2-m^2) where that sum is over m, from 1 to Infinity but not equalling n (the denominator would be 0 then). It can be solved explicitly, but again, I have no clue where to start. Thanks for any pointers!