12-4

> restart;

> with(plots):with(plottools):

Warning, the name changecoords has been redefined

> x1:=tan(t):;

> y1:=sec(t):;

> z1:=0:;

> x:=cos(s)*x1-sin(s)*z1:;

> y:=y1:;

> z:=sin(s)*x1+cos(s)*z1:;

> a:=plot3d([x,y,z],s=0..2*Pi,t=0..Pi/2-0.3,scaling=constrained):

> b:=plot3d([x,-y,z],s=0..2*Pi,t=0..Pi/2-0.3,scaling=constrained):

> p:=display(a,b):

> p;

> vrml(p,"c:/program files/maple 6/beauty/12-4.wrl",background_color=white);

>