Third circle theorem

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Angles in the same segment


Third circle theorem:

Compare the sizes of angles α & β, as you use the cursor to move point C or D around the circumference.
It doesn't change either angle β- they stay the same!
What is the effect of moving point E?
And finally, what happens when you move point B?

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If you need them, the seven circle theorems here

Tim Devereux, Created with GeoGebra