Conic Sections/Ellipse

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 $\frac{(x-h{)}^2}{a^2}+\frac{(y-k{)}^2}{b^2}=1$ where the center is at $(h,k)$ and the axes have lengths $2a$ and $2b$.$x/a$

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.