1. The problem statement, all variables and given/known data http://img94.imageshack.us/img94/3853/physicse.jpg [Broken] 3. The attempt at a solution I kept y fixed, and so I ended up with the following equation: Integ[dU/U] = Integ[x] And we end up with: U(x,y) = e^x * g(y) To solve g(y), we sub the solution into the 2nd PDE provided to give: d/dy[e^x * g(y)] = y[e^x * g(y)] Dividing through by e^x: d/dy [g(y)] = y*g(y) I was stuck at this point, so took a peek at the answers to find the lecturer wrote: => ln[g(y)] = 1/2*y^2 + c How did he come to that? I can't solve this equation, could someone please help me out? Thank you very much!