Focal Chord

Focal Chord

A chord of the ellipse passing through a focus is called a focal chord.

For the focus $$S_2(c,0)$$, if the endpoints have eccentric angles $$\theta_1,\theta_2$$, then the focal-chord condition is:

$$\cos\theta_1+\cos\theta_2=-\frac{2c}{a}$$

Usage

- Used to establish the relation between the parameters of the endpoints of a focal chord.