If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.
If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.
Foci of an ellipse
Learn about the foci of an ellipse, which are two points for which the sum of the distances from any point on the ellipse is constant.
Sal explains how the radii and the foci of an ellipse relate to each other, and how we can use this relationship in order to find the foci from the equation of an ellipse.
Given the major and minor radii of an ellipse, find its foci.
Given the equation of an ellipse, find its foci.
Given the foci of an ellipse (and some other feature), find its equation.