How Can You Prove <)APB+<)CPD=180' in a Base-Quadrilateral Pyramid?

[menager31]

There is a base-quadrilateraled pyramid ABCDS , which base is quadrilateral ABCD. Inscribed sphere is tangent in point P on the ABCD wall. Proof that

<)APB+<)CPD=180'


I don't like geometry and i really don't know how to start.

 

[einstein_fan]

I guess you are participating both Physics and Mathematics Polish Olympiad... Try to ask this question on the website www.matematyka.org

 

[menager31]

no I'm not

 

[einstein_fan]

That's interesting, because only about 2-3 of your threads are not connected to problems given to solve on the first levels of those olympiads...