## Thomas' Calculus 13th Edition

Comparing to Table 12.1, we recognize the form of an Elliptical paraboloid (with y and z interchanged; y is negative). This means that it opens along the y-axis (instead of the z-axis), and the minus tells us that it opens in the -y direction. The cross sections with $x=k$ and $z=k$, are parabolas, and with $y= -k$ they are circles (special cases of parabolas).