How to make diagonals for Geogebra

I am a teacher. I want to show my students about basic polygons. The topic I will focus are vertices, number of sides and diagonals. I have problem in recognizing the feature of the Geogebra where I want the polygons to show the diagonals too when everytime I changed n1.

I already made the sliders to connect with the polygons. when n1= 12 then the vertices is 12. So, is there anyone knows how to make the diagonals in the polygons connects along with the sliders?

Thank you.