Tangent to an ellipse

A line on the outside of an ellipse that touches it at just one point
Try this Drag any orange dot. Note the tangent line touches at just one point.

The blue line on the outside of the ellipse in the figure above is called the "tangent to the ellipse".    Another way of saying it is that it is "tangential" to the ellipse. (Pronounced "tan-gen-shull"). It is a similar idea to the tangent to a circle.

The line barely touches the ellipse at a single point. If the line were closer to the center of the ellipse, it would cut the ellipse in two places and would then be called a secant. In fact, you can think of the tangent as the limit case of a secant. As the secant line moves away from the center of the ellipse, the two points where it cuts the ellipse eventually merge into one and the line is then the tangent.


Other ellipse topics