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

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

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

> 
> 
