PS

NOTE: You can download the individual movies from here.
We have presented 4 methods for this task. The methods are clearly related and it is a moot point whether they are really distinct. However, we would be pleased to hear about more methods, distinct or not. Please email MT, post comments on the MT/ATM website or send an email to info@mathsmed.co.uk

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For those seeking something more interactive, we attach a link to one of the GeoGebra files used to create the animations:
GeoGebra file
[Use the two SLIDERS to animate the diagram.]