> with(plots):with(plottools):

> x:=cos(t):

> y:=sin(t):

> u:=x/sqrt(3):

> z:=(1-s)*u+s*(-1.5):

> a:=plot3d([x,y,z],s=0..1,t=Pi/2..3*Pi/2,scaling=constrained,grid=[5,50]):

> b:=plot3d([-x,y,z],s=0..1,t=Pi/2..3*Pi/2,scaling=constrained,grid=[5,50]):

> c:=display(a,b):

> d:=rotate(c,0,2*Pi/3,0):

> e:=rotate(c,0,4*Pi/3,0):

> h:=display(c,d,e):

> h;

> vrml(h,"C:/My Documents/trfa/wrl/11-4.wrl",background_color=white);

>