Conic Sections - The Circle
On an (x, y) graph a circle can have this shape:
If a plane intersects the cone when it is perpendicular to the axis, the conic section is a circle. Actually, a circle is a special case of an ellipse. This is shown below:
Here is a VRML animation that shows several possibilities for forming a circle by intersecting a cone and a plane. (For help with VRML go here.)
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