0.5*(82-24) = 20 diagonals
If all of the diagonals are drawn from a vertex of an octagon, how many triangles are formed
it really isn't hard 5
5 triangles are formed.
There are 20 diagonals
16 diagonals* * * * *5. To all vertices except itself and one each on either side.
None, if it is an irregular octagon.