1. The problem statement, all variables and given/known data Please take a look at the example at the bottom (at eq. 18:18, at page 619): http://books.google.dk/books?id=9p6...g=iAUGf-f9d5uHRwwYZnpFpA8HJDA&hl=da#PPA619,M1 Q1: In case (ii), why do they add g(x^2+y^2)? Q2: Why do they not add it in case (i)? Q3: In case (ii), if I chose f(p) = p + 1 instead of f(p) = 2p, then the solution would be u(x,y) = 1+ x^2 +y^2 + g(x^2 + y^2), right? I hope you can help me; I find this really hard to understand, and I've spent hours trying to find out, but I find that the book is poorly written. They don't emphasize the important things at all, and the reader is left behind with so many questions. Thanks in advance.