Second circle theorem:[br][br]Try moving the point P about. Where does P have to[br]be for angle α to be acute? and where must P be for angle α to be[br]obtuse? So where must P be to make angle α  =  90 degrees?

(Now go on to [url=https://www.geogebra.org/material/edit/id/597681]CT2b[/url] - the other Geogebra worksheet for the second circle theorem)