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.

In this movie, the side AB starts off as 8 units long. We see what happens as its length increases to 11 units and then gradually decreases all the way down to 0. Before showing the movie, ask students to predict what will happen to the square as AB starts to increase.

On the next page we show what is essentially the same movie, but with pauses at salient points. You might prefer to show that movie first.

You might want to ask students to explain why EFGH turns out to be a square.
This is quite a difficult thing to do since, from looking at the diagram, it just seems 'obvious'. But why is it a logical consequence of the fact that we started with a rectangle and drew its angle bisectors? [As we see later, we get a different shape when we start with a parallelogram.]