# Conjugate Diameters

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## conjugate diameters

[′kän·jə·gət dī′am·əd·ərz]
(mathematics)
For a conic section, any pair of straight lines either of which bisects all the chords that are parallel to the other.
For an ellipsoid or hyperboloid, any three lines passing through the point of symmetry of the surface such that the plane containing the conjugate diameters (first definition) of one of the lines also contains the other two lines.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Conjugate Diameters

Two diameters of a conic are said to be conjugate if each of them bisects the chords of the conic that are parallel to the other. Conjugate diameters play an important role in the general theory of conies. In the case of a parallel projection of an ellipse into a circle, conjugate diameters of the ellipse are projected into a pair of mutually perpendicular diameters of the circle.