Question 10 (13 marks) Let f(z, y) = ry try. (a) Calculate lim f(x, y). (z,N) +(1,2) (b) Find the directional derivative of f at (1,2) in the direction = anticlockwise from the positive r-axis.(c) Starting at (1, 2), in which direction does f decrease the fastest? Give your answer as a unit vector. (d) Find # at t = 0 given r(t) = tcosh(2t) and y(t) = tet + 2e