1. Plural of directrix; a fixed line used in the mathematical definition of a conic section (such as a parabola or ellipse), in relation to a focus point.
Usage: mathematics; technical
2. Plural of directrix; a woman who directs or manages; a female director.
Usage: archaic or rare

Examples

• In the study of parabolas, the directrixes and foci determine the shape of the curve.
• The equation of an ellipse involves both its foci and its directrixes.
• Students learned how to find the directrixes of a conic section using the eccentricity.
• The distance from any point on the parabola to the focus equals its distance to the directrix.
• Multiple directrixes are used when analyzing different conic sections in analytic geometry.