## Calculus 8th Edition

(a) The value of $z$ of the graph decreases at the point $(-1, 2)$ as the value of $x$ increases from the point along the x- axis, this represents the negative values of $f_{x}$. Thus,$f_{x} (-1,2)$ is negative. (b) The value of $z$ of the graph decreases as the value of $y$ increases near the point $(-1, 2)$ , this represents the negative values of $f_{y}$. Thus,$f_{y} (-1,2)$ is negative.