Illustration of the law of corresponding cones (l.c.c) for two tangent ellipses and their confocal hyperbolae ; (a): 3D representation: the two cones which lie on the two ellipses (blue cones) have one common generatrix; likewise for the two cones, which lie on the two hyperbolae (red cones); adapted from ; (b): 2D representation: the line joining the visible focus F1 of one ellipse to the invisible focus (not physical) of the other F2′ goes exactly through the tangential point M between the two ellipses; adapted from .