Sketch of ellipse concepts

A sketch of the concepts in an ellipse. The focal points (foci) are the major radius (a) distance from the top (b) to an intersection point on the major axis. Distance from foci-to-ellipse-to-foci is always the full length of the major axis. This is why we draw an ellipse using a string and two pins at the foci (see video below).

Image by Dave South

Posted to Ellipse Calculator

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