Electrical Machines and Transformers
Good morning!

To get to the result that line to line voltage(Vl) is phase voltage(Vp)*3^1/2, you need to analize the phasorial diagram:



Follow the same procedure to find the relation between Vp and Vl for any poliphase electric system.
For hexaphase system you´ll find Vl=Vp, thats because the angle between phase voltages is 60º.

Have a good day!