plotfunc3d(x*y^2)

plotfunc3d(9-x^2-2*y*(y-2),a,

       x=-5..5,y=-5..5,

       ViewingBoxZRange=-20..20,

       a=-20..10)

plotfunc2d(9-2*y*(y-2))

plotfunc3d(sin(x*y^2/20))