THis is more of a proof problem. I worked the problem up until the point where it begins a replacement for r/R. The book has enough examples to understand it up until that point.. but then it jumps from radii to simply the n term. I got a copy of the solution from the professor and I just don't get why they do that. I can't integrate that function in any way to get that new n-based equation. Any ideas on what's going on? I cant find anything in the book on that.