Editing Parallelogram (section)

===Tangent parallelogram of an ellipse===

For an [[ellipse]], two diameters are said to be [[Conjugate diameters|conjugate]] if and only if the [[tangent line]] to the ellipse at an endpoint of one diameter is parallel to the other diameter. Each pair of conjugate diameters of an ellipse has a corresponding [[tangent parallelogram]], sometimes called a bounding parallelogram, formed by the tangent lines to the ellipse at the four endpoints of the conjugate diameters. All tangent parallelograms for a given ellipse have the same area.

It is possible to [[Compass and straightedge constructions|reconstruct]] an ellipse from any pair of conjugate diameters, or from any tangent parallelogram.