1. The problem statement, all variables and given/known data If α is an arbitrary constant and a a fixed constant show that xcos α + ysin α = a is the complete primitive of the equation (y - xdy/dx)^2 = a^2( 1 + (dy/dx)^2) 2. Relevant equations 3. The attempt at a solution FIrst I found the first derivative by differentiating implicitly, cosα + (dy/dx)sinα = 0 But now I'm looking for something to sub to try and get the differential equation and eliminate the arbitrary constants, but I keep getting into a loop and cancelling everything basically... Please help.