[Mentor's note: This thread does not use the standard homework template because it was moved here from one of the non-homework forums.] Hi, Looking for help on what to do next. Question (it's in two parts but part 1 is like two lines): Part 1: http://imgur.com/BwyNwsE  Part 2: http://imgur.com/LrIh4IP  Normally my approach is to evaluate the double derivative on the LHS and rearrange until I can equate it to the RHS. This time I'm unsure what to make of Φ as it's not expressed in terms of x and y. What am I looking at and how do I go about solving it? Thanks.