Un problème de papillon — Inégalité dans un cercle | Tangente

The ellipse and its many features

Although descriptive geometry provides laborious methods for constructing an ellipse with straightedge and compass (see the article "Albrecht Dürer and technical drawing"), other, more conventional methods also exist. A point on the curve, the center, foci, axes and tangents: let's take a quick tour of the available techniques!

Butterfly theorem: circle and chords | Tangente

Reim's theorem: two intersecting circles | Tangente

Frégier point: perpendicular chords | Tangente