Problem 6 Directional derivatives. (i) Find the directional derivative of the function /(r, y) = In(2x2 + 3y?) at the point (-1, 1) and in the direction (3, -4)- (ii) Let /(x, y) = y' - cosry. Find all directions u of unit length such that the directional derivative at the point P = (0, 1) is 1