*Macmillan Science Library: Mathematics*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

This section contains 525 words(approx. 2 pages at 300 words per page) |

## Conic Sections

Imagine there are two cone-shaped paper drinking cups, each fastened to the other at its point, or vertex. The figure that would result is described mathematically as a right circular cone (sometimes called a double cone), which is formed by a straight line that moves around the **circumference** of a circle while passing through a fixed point (the vertex) that is not in the plane of the circle.

If a right circular cone is cut, or intersected, by a **plane** at different locations, the intersections form a family of plane curves called **conic sections** (see the figure). If the intersecting plane is parallel to the base of the cone, the intersection is a circle—which shrinks to a point when the plane has moved toward the cone's tip and finally passes through the vertex. If the intersecting plane is not parallel to the base, passes...

This section contains 525 words(approx. 2 pages at 300 words per page) |