> N[3]:=(xi,eta)->(1+xi)*(1-9*xi^2)*(1+eta)*(1-9*eta^2)/256;

  N[3] := (xi, eta) ->

                                2                      2
        1/256 (1 + xi) (1 - 9 xi ) (1 + eta) (1 - 9 eta )

> plot3d(N[3],-1..1,-1..1,grid=[15,15], axes=boxed, scaling=constrained,
> style=patch,orientation=[-60,60]);

> 
> 
