1. The problem statement, all variables and given/known data The question asks: f(x,y) = 3xy+5y^3/[x^2+y^2] when (x,y) =! (0,0) f(x,y) = 0 when (x,y) = (0,0) what is df/dy at (0,0)? 2. Relevant equations 3. The attempt at a solution I'm not sure what the answer is. At 0,0 f(x,y) is 0, so it's simply a point and the function is not continuous at the point, therefore df/dy doesn't exist?