# Focus-Directrix Property of an Ellipse with Dandelin Spheres

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This Demonstration shows a plane cutting a cone in an ellipse; the two spheres tangent to the plane and the cone meet the cone in two circles. The spheres meet the plane at the foci of the ellipse. The directrices are the lines where the cutting plane meets the planes of the circles of contact.

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Contributed by: Khalid Bin Walid (August 2014)

Open content licensed under CC BY-NC-SA

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## Details

detailSectionParagraph## Permanent Citation

"Focus-Directrix Property of an Ellipse with Dandelin Spheres"

http://demonstrations.wolfram.com/FocusDirectrixPropertyOfAnEllipseWithDandelinSpheres/

Wolfram Demonstrations Project

Published: August 6 2014