Conjugate

Conjugate, a term employed in geometry to denote certain pairs of points, lines, or surfaces that possess harmonic relations to each other. The harmonic conjugate of a point with regard to two others in the same line is that point the reciprocal of whose distance from the given point is the mean of the reciprocals of its distances from the other two. Conjugate diameters of a conic section are such that each is parallel to the tangents at the extremity of the other; each will bisect all chords parallel to the other.