1. The problem statement, all variables and given/known data w= f(x,y) x = u + v Verify that Wxx - Wyy = Wuv y = u - v 2. Relevant equations 3. The attempt at a solution I know how to find Wu or Wv but I have no idea on how to proceed to find the 2nd order derivative (or 3rd,4rth etc.. obviously). I assume this somehow uses the chain rule but I had no idea on how to apply it in this situation. Thank you!