Problem 6. (15%) Let f(x, y) = r- 6ry + 2y. We would like to find all local extrema of f(x,y). (a) (10%) Find all critical points of f(x, y). (b) (5%) Determine if f attains local maximum, local minimum or neither at each critical point. (Hint: Discriminant D=fzz(x, y)f(x,y) - [Szy(x,y)])