Find f , f, and f., and evaluate each at the given point. f ( x, y, z) = x2y3 + 2xyz -5yz, (-3, 1, 3) f ( x, y, z) = fu (x, y, z) = f- ( x, y, z) = fx( - 3, 1, 3) = f( - 3, 1, 3) = f ( - 3, 1, 3) =