Double-click on the movie to PLAY.

Click once to PAUSE.

RELOAD the page or double-click to return to the START of the movie.

Here we show the trace of a point Q as it moves from B to D, and a trace of its image.

The image points appears to lie on an arc of a circle. What conjectures can we make about the circle?

On the next page we move Q through a more extensive set of points on the line through BD, which results in a more extensive arc for the image points.