> N[4]:=4*(1-xi-eta)*xi;
> plot3d(N[4],xi=0..1,eta=0..1-xi,axes=boxed,orientation=[-130,60],
> style=wireframe,color=black,thickness=1,scaling=constrained,tickmarks=
> [3,3,3]);

                     N[4] := 4 (1 - xi - eta) xi


> 
