Hyperboloid of Two Sheets:

> implicitplot3d( -x^2-y^2+z^2=1, x=-3..3, y=-3..3, z=-3..3, grid=[9,9,9], orientation=[30,80], scaling=constrained, axes=boxed );

>

> plot3d( { sqrt(1+x^2+y^2), -sqrt(1+x^2+y^2) }, x=-3..3, y=-3..3, view=[-3..3,-3..3,-3..3], orientation=[30,80], scaling=constrained, axes=boxed );

>