Definition:Ovals of Cassini/Focus

Definition
Consider the cvals of Cassini defined as the locus $M$ described by the equation:
 * $P_1 M \times P_2 M = b^2$

for constant $b$


 * Ovals-of-Cassini.png

Each of the two points $P_1$ and $P_2$ can be referred to as a focus of the ovals.