> restart: with(plots):
> f:= x^2-y^2;
> plot3d( f, x=-3..3, y=-3..3, axes=normal);
# Warning, the name changecoords has been redefined
                                2    2
                          f := x  - y 

> plot3d( sin(x*y), x=-5..5, y=-5..5, axes=normal,numpoints=2000);

> plot3d( x*(x^2-3*y^2), x=-3..3, y=-3..3, axes=normal);

> plot3d( x^3-y^3, x=-3..3, y=-3..3, axes=normal);

> plot3d( x^2*sin(y), x=-4..4, y=-6..6, axes=normal);

> plot3d( sin(y)*exp(x), x=-4..4, y=-6..6, axes=normal);