This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Ellipse Properties of Directrix and String Construction.svg ellipse including The distance to focus from the centre is the eccentricity multiplied by the semimajor axis The distance from one focus to the other via any point on the ellipse is always The distance from point on the ellipse to focus is always proportional to the distance