# Eccentricity of a Conic Section

## Eccentricity of a Conic Section

Ratio of the distance |PF$$_{1}$$| between a point P of a conic section and a focus F$$_{1}$$ and the distance |PB| from the corresponding directrix.

### Notation

The eccentricity of a conic section is denoted as “e”, which is read “eccentricity”.

In the case of an ellipse, 0 < e < 1.

In the case of a parabola, e = 1.

In the case of a hyperbola, e > 1.