> N[12]:=(xi,eta) -> 9*(1+3*xi)*(1-xi^2)*(1-eta^2)/16;

                                                   2          2
      N[12] := (xi, eta) -> 9/16 (1 + 3 xi) (1 - xi ) (1 - eta )

> plot3d(N[12],-1..1,-1..1,grid=[15,15],axes=boxed,scaling=constrained,
> style=patch,orientation=[-60,60]);

> 
> 
