5 12 f ( x, y ) = x2 In(y), P ( 4, 1 ), U = - + 13 13 (a) Find the gradient of f. VA ( x, y) = 2x In(y), (b) Evaluate the gradient at the point P. Vf ( 4, 1 ) = (0, 16) (c) Find the rate of change of fat P in the direction of the vector u. 80