Conjugate diameters
![Two conjugate diameters of an ellipse. Each edge of the bounding parallelogram is parallel to one of the diameters.](/Images/godic/202501/06/Conjugate_Diameters.svg3824.png")
![For any φ, the indicated diameters of the circles and hyperbolas are conjugate.](/Images/godic/202501/06/Orthogonality_and_rotation.svg3824.png")
In geometry, two diameters of a conic section are said to be conjugate if each chord parallel to one diameter is bisected by the other diameter. For example, two diameters of a circle are conjugate if and only if they are perpendicular.