Foci
of an Ellipse
Two fixed points on the interior of an ellipse used in the formal definition of the curve. An ellipse is defined
as follows: For two given points, the foci, an ellipse is the locus of points such that the sum of the distance to each focus is constant.
Note:
If the interior of an ellipse is a mirror, all rays of light
emitting from one focus reflect off the inside and pass through
the other
focus.
See
also
Directrices
of an ellipse, foci
of a hyperbola,
focus of a parabola, focal radius
