1. The problem statement, all variables and given/known data f(x.y)=4x^2-y^2 2. Relevant equations Ʃ partial derivative components(?) 3. The attempt at a solution The solution when θ=pi and f(1,-1) is -8. Does this mean that one of the coordinates of this function is (1,-1,-8)? What exactly is the directional derivative, and what does the solution represent?