Answer
(a) Positive
(b) Negative
Work Step by Step
(a) The second derivative shows concavity. As we move along the x-axis at the point $(-1, 2)$, the graph is shown to be concave up .
This shows that $f_{xx} $ is positive.
(b) The second derivative shows concavity. As we move along the y-axis at the point $(-1, 2)$, the graph is shown to be concave down.
This shows that $f_{yy} $ is negative.
