1. The problem statement, all variables and given/known data (dy/dx) - cos2(x-y) = 0 2. Relevant equations 3. The attempt at a solution I'm unsure where to start this. This isn't a liner equation of form (dy/dt) + p(t)y = g(t) ; and it's not separable nor an exact equation. Is it illegal to make this (dy/dx) - cos2(x) + cos2y = 0 ??? Thanks for your time.