The Directrix

I. The Parabola

The parabola has one focus and one directrix.

Locus Definition:
A parabola is the locus of points equidistant from its focus and its directrix.

II. The Ellipse

The ellipse has two foci and two directrices.

Locus Definition:
An ellipse is the set of points whose distance from the focus is equal to e times the distance to the directrix ( where 0 < e < 1).

III. The Hyperbola

The hyperbola has two foci and two directrices.

Locus Definition:
An hyperbola is the set of points whose distance from the focus is equal to e times the distance to the directrix ( where e > 1).

Send any comments or questions to: David Pleacher