Tangents to an Ellipse from a Given Point
This Demonstration shows a construction of the tangents to an ellipse from the given external point . The foci of the ellipse are at , . Let be the circle with center at the midpoint of the ellipse, with radius equal to the semimajor axis. Let be the circle with the diameter from the point to the focus . Then the two intersections of these circles are points on the tangents to the ellipse.