Double-click on the movie to PLAY.

Click once to PAUSE.

RELOAD the page to return to the START of the movie.


Another method:

We can draw a circle with diameter PQ through P, A, Q and M (where M is the midpoint of the square). Why?

Angle PQM = 45˚.

Angle PAM = angle PQM because they are subtended on the circle by the same chord.

So the red line bisects the angle at A.