Chapter 10 - Parametric and Polar Curves - 10.4 Conic Sections - 10.4 Exercises - Page 750: 3

$$\eqalign{ & {\text{A hyperbola is the set of points in a plane whose distances from }} \cr & {\text{two fixed points have a constant difference}},{\text{ either }}2a{\text{ or}} - 2a \cr & {\text{As with ellipses}},{\text{ the two fixed points are called foci.}} \cr} $$

$$\eqalign{ & {\text{A hyperbola is the set of points in a plane whose distances from }} \cr & {\text{two fixed points have a constant difference}},{\text{ either }}2a{\text{ or}} - 2a \cr & {\text{As with ellipses}},{\text{ the two fixed points are called foci.}} \cr} $$