In the applet below you can experiment with the locus definition of an ellipse: the locus of points, P, such that the sum of the distances from two fixed points, called the foci , is constant.
Drag E below and observe the path that F and G follow. After points have been traced, clicking the red X in the bottom right corner will erase the traced points.
The sketches on this page were created with a prototype of JavaSketchpad, a World-Wide-Web component of The Geometer's Sketchpad. Copyright ©1990-1998 by Key Curriculum Press, Inc. All rights reserved. Portions of this work were funded by the National Science Foundation (awards DMI 9561674 & 9623018).