---
tag: 0E5CXYNEPX
kind: concept
name: Directrix
msc: [51N20]
sources:
  - url: https://en.wikipedia.org/wiki/Conic_section
    locator: Eccentricity, focus and directrix
---

## Summary

A directrix of a conic is a line with the following property. For each point of the conic, the distance to a focus divided by the distance to the line is the same constant. This constant is the eccentricity.