Directrix of a Parabola

Directrix of a Parabola

A line perpendicular to the axis of symmetry used in the definition of a parabola. A parabola is defined as follows: For a given point, called the focus, and a given line not through the focus, called the directrix, a parabola is the locus of points such that the distance to the focus equals the distance to the directrix.

 

 

Example:

This is a graph of the parabola with all its major features labeled: axis of symmetry, focus, vertex, and directrix.

 

See also

Directrices of an ellipse, directrices of a hyperbola