研究所、轉學考(插大)-微積分題庫下載題庫

4. Let f(x, y) = 4 + x³ + y³ - 3xy. Which of the following must be true?
(A) f has a local maximum at (0,0).
(B) f has a local minimum at (1,1).
(C) At the point P(1,0), f have the maximum rate of change in the direction (1,-1).
(D) The maximum rate of change at the point P(1,0) is .