Definition of directrix in English:

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Pronunciation: /dɪˈrɛktrɪks/
Pronunciation: /dʌɪˈrɛktrɪks/

noun (plural directrices /dɪˈrɛktrɪsiːz/ /dʌɪˈrɛktrɪsiːz/)

A fixed line used in describing a curve or surface.
Example sentences
  • In the following, the feet of perpendiculars dropped from points A, B, etc. on the parabola to the directrix will be denoted A ’, B ’, etc.
  • The focus and directrix of a hyperbola were considered by Pappus.
  • The directrix is used in the construction, which follows, mutatis mutandis, the same course as the above construction in the case of the ellipse.


Early 18th century: from medieval Latin, literally 'directress', based on Latin dirigere 'to guide'.

For editors and proofreaders

Line breaks: dir|ec¦trix

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