The Function F(x, Y)has a Local Maximum at (-1, 1) $f _ { x y } ( - 1,1 )$

Multiple Choice

The function f(x, y) has a local maximum at (-1, 1) . What can you say (if anything) about the values of $f _ { x y } ( - 1,1 )$ ?

A) Nothing.
B) It is undefined or equal to zero.
C) It cannot be greater than zero.
D) It is equal to zero.