36-42 DIRECTIONAL DERIVATIVE off at P in the direction of a. Find it and make a sketch. 36. f = 2x² + 2y2, P: (3, 3), a = [-1, -3] a = [2, 1] 37. f = x - y, P: (4, 5), 2 38. f = x² + y² + z², 2 P: (2, 2, -1), a = [1, 1, 3] 2 2 39. f = 1/√x² + y² + ₂², a = [1, 1, 1] 10 P: (3, 0, 4),
