Focus-Directrix Property

Focus-Directrix Property

For any point $$p$$ on an ellipse:

$$\frac{PS}{PM}=e$$

Terminology

- $$s$$ → Corresponding focus.

- $$m$$ → Foot of the perpendicular from $$p$$ to the corresponding directrix.

- $$e$$ → Eccentricity.

Usage

- Used to express the ellipse through its focus-directrix definition.