An interactive applet and associated web page that demonstrate the tangent to an ellipse. An ellipse is shown and a tangent line that touches it at the one point. The user can drag the tangent point around the ellipse and the tangent follows. The ellipse can be reshaped by dragging the foci. The applet shows the fact that the two lines from the foci to the tangent meet it at equal angles.

The web page has the written properties of the tangent and links to other pages defining the various properties of an ellipse and to some ellipse constructions.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.