Answer
Elliptical paraboloid.
Work Step by Step
Divide with 4,
$\displaystyle \frac{z}{4}=\frac{x^{2}}{2^{2}}+\frac{y^{2}}{1^{2}}$
Compare with Table 12.1 and conclude that this is an elliptical paraboloid.
The traces in xz and yz planes are parabolas.
The traces in planes parallel to the xy plane are ellipses.
