> N[7]:=(xi,eta) -> -1*(1+xi)*(1-9*xi^2)*(1-eta^2)/16;

                                                   2          2
      N[7] := (xi, eta) -> -1/16 (1 + xi) (1 - 9 xi ) (1 - eta )

> plot3d(N[7],-1..1,-1..1,grid=[15,15],axes=boxed,scaling=constrained,
> style=patch,orientation=[-60,60]);

> 
> 
