This page uses **JavaSketchpad**, a World-Wide-Web component of *The Geometer's Sketchpad.* Copyright © 1990-2001 by KCP Technologies, Inc. Licensed only for non-commercial use.

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Ellipses

Here you see concentric circles and a point *P* on the outer circle. Segment *OP* meets the inner circle in a point which is the vertex opposite *P* in a rectangle. The loci of the other two vertices are ellipses.
During animation, drag the red points.

For more, see *GEOMETRY IN ACTION*, Chapter 4, Project 4.