Worth having a look at [url=https://www.geogebra.org/material/edit/id/597519]CT2a[/url] first; then... [br][br]What happens to angle α as you move P? [br][br](Bit dull, as I expect you've worked out that there is an angle bigger than acute, but smaller than obtuse....)

If you need it, this theorem is set out [url=http://www.timdevereux.co.uk/maths/geompages/8theorem.php#th2]here[/url] [br]and all the theorems are summarised [url=http://www.timdevereux.co.uk/maths/geompages/8theorem.php]here[br][/url] [br]Tim Devereux, Created with GeoGebra