> restart:

> a:=3:b:=4:c:=sqrt(a^2+b^2):

> r:=c+a*cos(t):x:=r*cos(s):y:=r*sin(s):z:=a*sin(t):

> u:=solve(b*z=a*x,s):

> with(plots):

Warning, the name changecoords has been redefined

> plot3d([x,y,z],s=-u..u,t=0..2*Pi,scaling=constrained);

> restart:

> a:=3:b:=4:c:=sqrt(a^2+b^2):

> x0:=c*cos(t):y0:=a+c*sin(t):z0:=0:

> s:=arccos(b/c):

> x1:=x0*cos(s)-z0*sin(s):y1:=y0:z1:=x0*sin(s)+z0*cos(s):

> x:=x1*cos(u)-y1*sin(u):y:=x1*sin(u)+y1*cos(u):z:=z1:

> plot3d([x,y,z],t=0..2*Pi,u=0..Pi,scaling=constrained);

> restart:

> with(plots):

> tubeplot([cos(2.5*s),sin(2.5*s),0],s=0..5*Pi,scaling=constrained,radius=0.6,grid=[30,50],lightmodel=light2);

> restart:

> r:=3+cos(2.5*s):

> x:=r*cos(s):y:=r*sin(s):

> z:=sin(2.5*s):

> with(plots):

Warning, the name changecoords has been redefined

> tubeplot([x,y,z],s=0..5*Pi,scaling=constrained,radius=0.4,grid=[100,10],lightmodel=light2);

> restart:

> r:=3+cos(s/3):

> x:=r*cos(s):y:=r*sin(s):

> z:=sin(s/3):

> with(plots):

Warning, the name changecoords has been redefined

> tubeplot([x,y,z],s=0..6*Pi,scaling=constrained,radius=0.4,grid=[100,10],lightmodel=light2);

> restart:

> p:=2*Pi/3:

> r1:=3+cos(t/3):x1:=r1*cos(t):y1:=r1*sin(t):z1:=sin(t/3):

> r2:=3+cos(t/3+p):x2:=r2*cos(t):y2:=r2*sin(t):z2:=sin(t/3+p):

> x:=(1-s)*x1+s*x2:y:=(1-s)*y1+s*y2:z:=(1-s)*z1+s*z2:

> plot3d([x,y,z],s=0..1,t=0..6*Pi,scaling=constrained,grid=[5,100],lightmodel=light2);

>