4. Let f (1:, y) = 1:3 + e" sin(32y). (a) (4 pics) Find the rate of change of f(z,y) at. (1,0) in the direction of u = (2, 1). (Noni: u is not a unit vector). (b) (4 pts) Find all direction(3) in which the rate of change of f(:c, y) at the point; (1,0) is 0. Give your nal answer as unit vector(s)