Find the directions in which the function increases and decreases most rapidly at Po. Then find the derivatives of the function in these directions. f(x,y,z) = (x/y) - yz, Po(4, - 1, - 3) The direction in which the given function f(x,y,z) = (x/y) - yz increases most rapidly at Po (4, - 1, - 3) is u = + (Type exact answers, using radicals as needed.)