Double-click on the movie to PLAY.

Click once to PAUSE.

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

M2

Here the red line is rotated through 90˚.

Which point is the centre of rotation?

It looks as though the image goes through K and C and A [but we really need to prove it - the animation is just a demo].

If this is true, ie if the image is a diagonal of the other two squares, then we can say:

angle BAP = angle CKP = 45˚

and so the red line bisects the angle at A.