Find Daf at P where u is the unit vector in the direction of v. (a) f(x, y) = el sin y, P = (1, ; ), 0 = i (b) f(x, y) = In(x2 + y?), P = (1, -1), 0 = (3, 4) (c) f(x, y, z) = 3x 23 + 4xy - 322, P = (3, 2, 1), v = (1, 1, 1)