Construct various crosssections of a cone.  

Construct onehalf of the tangent cone of a sphere.  
Given three spheres S_{1}, S_{2}, S_{3}, let P_{1}, P_{2}, P_{3} be the points of contact of one common tangent plane of the spheres, and Q_{1}, Q_{2}, Q_{3} the points of contact of the other common tangent plane of the spheres. Show that the lines P_{1}P_{2} and Q_{1}Q_{2}, meet at a point R_{12}, the lines P_{2}P_{3 }and Q_{2}Q_{3 }meet at a point R_{23}, the lines P_{3}P_{1}, Q_{3}Q_{1}meet at a point R_{31}, and that the points R_{12}, R_{23} and R_{31}lie on a straight line. 
Construct a surface which appears as a triangle along the
xaxis, 
appears as a triangle along the yaxis,

apprears as an astroid along the zaxis 
Construct this pattern form by line segments joining [cos(t),0]
with [0,sin(t)] as t ranges over the interval [0,2p].
¡@ m:=[[cos(t),0],[0,sin(t)]]; 
Construct this pattern:
t:=Pi*n/100:x:=cos(t)1:y:=sin(t): 