Sums of angles by paper cutting

Sum of interior angles of a convex n-gon

https://www.youtube.com/watch?v=_yRDwYYjgOY

Sum of exterior angles of a convex n-gon

https://www.youtube.com/watch?v=JR-HVADDL74

Exterior angle theorem

https://www.youtube.com/watch?v=3-9jcdN-Eqw
https://www.youtube.com/watch?v=APX7sh7_PcU

Sum of interior angles of n-pointed star tips

https://www.youtube.com/watch?v=w4AUOgfW9NI