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.

**Movie A1**

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.

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.]