The distance (sometimes also denoted ) from the focus to the conic section directrix of a conic section. The following table gives the focal parameter for the different types of conics, where is the semimajor axis, is the distances from the origin to the focus, and is the eccentricity.

# Focal Parameter

## See also

Conic Section, Conic Section Directrix, Eccentricity, Focus, Semilatus Rectum, Universal Parabolic Constant## Explore with Wolfram|Alpha

## Cite this as:

Weisstein, Eric W. "Focal Parameter."
From *MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/FocalParameter.html