> p1:= plot3d([x, y, 16-4*x^2-y^2], x=0..2, y=0..4, axes=framed):

> p2:= plot3d([x, 2, 16-4*x^2-y^2], x=0..2,y=0..4, color=black, axes=framed):

> p3:= plot3d([1, y, 16-4*x^2-y^2], x=0..2,y=0..4, color=black, axes=framed):

> display({p1,p2});