申論題

5. (10 points) Let u(x,y) be a differentiable function with (4,1) = 2. dy Suppose that x = st and y= and define h(s, t) = u(x(s, t),y(s, t). At the point (2,2), find a unit vector u in the st-plane such that h increases most rapidly in the direction. (4, 1) = 1 and