## Calculus 8th Edition

(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.