Conic Sections/Ellipse

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[edit] Definition

The geometric definition of an ellipse is the locus of all points such that the distances from two points called foci add up to a constant. The general equation for an ellipse is where the center is at (h,k) and the axes have lengths 2a and 2b.

[edit] Reflection

Assuming a perfectly reflective perfect ellipse, any light emitted from a focus of an ellipse will be reflected to intercept the other focus. This property is exploited in "Whispering Galleries" where 2 people stand at the foci of an arbitrarily large elliptical room and can clearly hear each other whispering.