Definition:Ellipse

Parts of Ellipse

 * EllipseParts.png

Consider an ellipse $K$ whose foci are $F_1$ and $F_2$.

For convenience, let $K$ be aligned in a cartesian coordinate plane such that:
 * $F_1$ and $F_2$ are located on the X-axis
 * the midpoint of the line $F_1 F_2$ is located at the origin.