4. (12 points) Let f(x) be a (scalar valued) function of a single variable x satisfying f (0) 2, f'(0) = 1 where f'(x) = J Define a function g(x, y) = cos(x + y) . f(x) Find gx(0, 3) = :2(0, 3) and gy(0, ;) = (0, 5). gz (0, 5) gy (0, 5 ) =