A cone can be constructed from a circle and a point (the vertex of the cone) not in the plane of the circle. The surface of the cone is the set of points on all lines through the vertex and points on the circle. Alternatively, a moving line through the vertex and a point on the circle sweeps out the surface of a cone.
Because a cone is made from a line, Apollonius considered a cone as both parts (the two ice cream cones), and extending infinitely in both directions. The diagram shows only a finite part to avoid clutter.
Move the point on the circle to see the line move. Move the vertex to change the shape of the cone.
How to manipulate a Cabri3D diagram
