Talk:Confocal conic sections

b might be better
Since the grid of ellipses in the first graphic are spaced in even intervals of b, it might be better for the reader to use a different implicit formula. E.g. x² / (b² + c²) + y² / b² = 1. SharkD  &#9742;  19:17, 3 August 2018 (UTC)
 * Should also mention Elliptic coordinate system somewhere, since that's an example of confocal ellipses and hyperbolas. The formulas are again slightly different, however. SharkD   &#9742;  01:07, 5 August 2018 (UTC)

degenerate conics
I wonder if it's worth mentioning that a circle is a degenerate ellipse with its foci at the same point (the center) and likewise a pair of intersecting lines is a degenerate hyperbola with its two foci at the intersection. A concentric pair of circles, two pairs of intersecting lines with the same intersection, or a pair of intersecting lines with intersection at a circle center are in many ways similar to concentric conics. –jacobolus (t) 17:00, 11 January 2023 (UTC)