Confocal hyperbolas are Hyperbolas sharing common foci (left figure). The family of confocal hyperbolas covers
the plane simply, in the sense that there is a unique hyperbola passing through each
point in the plane (Hilbert and Cohn-Vossen 1999, p. 5). The figure on the right
shows confocal hyperbolas superimposed on confocal
ellipses, which form an orthogonal net of curves (Hilbert and Cohn-Vossen 1999,
pp. 5-6).
