Points around an Ellipse
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Given an ellipse with semimajor axis 
and semiminor axis 
, what is the locus of points 
in the plane of the ellipse such that there are two perpendicular tangents from 
to the ellipse? The answer is a circle of radius 
as illustrated in this Demonstration.
Contributed by: John Snyder (March 2011)
Open content licensed under CC BY-NC-SA
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"Points around an Ellipse"
http://demonstrations.wolfram.com/PointsAroundAnEllipse/
Wolfram Demonstrations Project
Published: March 7 2011
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