Answer
Elliptic paraboloid, opening downward (along z) with vertex at (0,0,9).
Work Step by Step
Trace in x=0: parabola, vertex at (0,0,9), opens down.
Trace in y=0: parabola, vertex at (0,0,9), opens down.
Traces when z is above 9: none.
Traces for z below 9: ellipses, $x^{2}+9y^{2}=k^{2}.$
Graph: Elliptic paraboloid, opening downward (along z) with vertex at (0,0,9).
