zero, for any tetrahedron, not just regular
None.
4 diagonals
27 diagonals
5 diagonals
8 diagonals
There are 9 diagonals in any hexagon!The hexagon does not have to be regular.
A regular 12 sided dodecagon has 54 diagonals.
Six.
54
There are 21 of them.
It has 20 diagonals and is made up by 6 triangles
0.5*(862-258) = 3569 diagonals