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.

PS

This shows the desired position for F (and a possible position for E).

As we know, F is not midway between D and D',
but what is the relationship of F to these points?

What about the relationship of F to other points?

As a final postscript, an elaborate trial and error approach is shown on the next page.