14L Partial derivatives: Directional Derivatives and the Gradient Vector 21. Find the gradient of f. b. Evaluate the gradient at the point P. c. Find the rate of change of f at P in the direction of the vector u. 3 4 12 = W3 .__ = f(ml y? z) yze :P 19(031' 1)? u Find the directional derivative of the function at the point P in the direction of the point Q. f(m1yl z) = 39 331222: P(23 F1: 1): Q(5: 1: 7) Find all points at which the direction of greatest rate of change of the function ay) =32+y2e2a=4yisi+i Answer i All points on the line '51 : a: + 1