> x:=xi*(2*xi-1)+2*sqrt(2)*(1-xi)*xi;

                                       1/2
               x := xi (2 xi - 1) + 2 2    (1 - xi) xi

> y:=eta*(2*eta-1)+2*sqrt(2)*(1-eta)*eta;

                                       1/2
             y := eta (2 eta - 1) + 2 2    (1 - eta) eta

> z:=1-(3-2*sqrt(2))*(xi+eta)-2*(sqrt(2)-1)*(xi+eta)^2;

                      1/2                   1/2                2
     z := 1 - (3 - 2 2   ) (xi + eta) - 2 (2    - 1) (xi + eta)

> plot1:=plot3d([x,y,z],xi=0..1,eta=0..1-xi,axes=normal,orientation=[-60
> ,80],shading=zgrayscale, tickmarks=[2,2,2]):
> plot2:=plot3d(1-xi-eta,xi=0..1,eta=0..1,axes=normal,orientation=[-60,8
> 0],view=[0..1,0..1,0..1],style=wireframe,color=black):
> plots[display]({plot1,plot2});

> rr:=x^2+y^2+z^2:
> rr:=expand(%):
> rr:=simplify(%):
> r:=+sqrt(%):
> L_[2]:=evalf(sqrt(int(int((1-r)^2,eta=0..1-xi),xi=0..1)));
Warning, computation interrupted

> l_[2]:=evalf(sqrt(int(int((1-r^2)^2,eta=0..1-xi),xi=0..1)));

                        l_[2] := 0.08014966047

> delta:=(1-r^2)^2-(1-r)^2:
> plot3d(delta,xi=0..1,eta=0..1-xi,axes=normal,orientation=[-60,80]);

> 
> 
