1. The problem statement, all variables and given/known data Given the function f(x) defined as: (x^3-y^3)/(x^2+y^2) if (x,y)≠(0,0) 0 if (x,y)=(0,0) Find the parcial derivatives of the function at the point (0,0). Is the function f differentiable? 2. Relevant equations 3. The attempt at a solution d/dx [ (x^3-y^3)/(x^2+y^2)] = [3x^2(x^2+y^2) - 2x(x^3-y^3)] / (x^2+y^2)^2 = = [x^4+3x^2*y^2+2xy^3]/(x^4+2x^2y^2+y^4) I can't find the way out of this indetermination... As to the second question, if the parcial derivatives exist then the function is differentiable in the point (0,0). I know from the solutions that the result will be 1 and -1. If anyone could point me in the right direction I'd really appreciate! Thanks!