I coudn't get the web code running. I defined a sphere by points. Using the command Equation(s) returns the corresponding equation if needed. My code is: with(geom3d): v0:=[0,0,0]: v1:=[5,0,0]: v2:=[3,6,0]: v3:=[1,1,6]: v4:=[10,10,5]: point(p0,v0),point(p1,v1),point(p2,v2), point(p3,v3), point(p4,v4), sphere(s,[p0,p1,p2,p3]): eqPlane:= z=4; plane(p,eqPlane,[x,y,z]); gtetrahedron(t, [p4, p1, p2, p3]); draw([s,p,t]); Now I would like to have a plot which shows just the intersection, which is a circle and a rectangle. Looking forward to hearing from you.

Hi Georgios, Thanks for you're answer. I didn't describe my problem properly. I know how to plot. The problem is that I would like to plot just the intersection of a sphere and a plane and also the intersection of a tetrahedron and a plane. In maple there exists the command intersection() for calculating the intersection of e.g. two spheres, but unfortunately intersection() is not working for a plane and a sphere. The intersection of a plane and a sphere is a circle, which I would like to plot later. Maybe you know how to do this. Many thanks!