> N[1]:=1-xi-eta;

                         N[1] := 1 - xi - eta


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

> 
