Definition:Lemniscate of Bernoulli/Focus

Definition
Consider the lemniscate of Bernoulli defined as the locus $M$ described by the equation:
 * $P_1 M \times P_2 M = \paren {\dfrac {P_1 P_2} 2}^2$


 * LemniscateOfBernoulli.png

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