in the planes x = k, y=k, z=k.
The given surface is an ellipsoid.
For x = -2, -1, 0, 1, 2 the traces are ellipses parallel to the yz-plane:
For z = 0 the trace is the ellipse 
,
which has vertices at 
If we set y = 0 the resulting equation is
. This is the equation of
an ellipse in xz-plane with vertices at 
The total is an ellipsoid:
by: gm