3. (16 pts) For (a) and (b) in this problem, you are not required to justify your answer. You need to justify (c). (a) (3 pts, only answer) Find the second-order Taylor polynomial of f (x, y) = 1 + 2x + 3y + 4x2 + 593 + 6xy' at (0, 0). (b) (3 pts, only answer) Let f (x, y) be as in (a). Find the second-order Taylor polynomial of g(x, y) = f(x, y) cos (2(x + y) ) at (0, 0). (c) (10 pts) Let U = (a, b) and g(x, y) be as in (b). Express Dag, which is by definition Do( Dog), using a and b