I'm going to answer this question....but I'm assuming an even spacing of the points {I actually don't know if this makes a difference, or not !!!!! }
When the number of points is even, it is quite complicated to determine the number of intersecting points.
When the number of points is odd.....number theory shows that no more than two diagonals ever intersect at any one point !!!.... and we have the following "formula" for the number of intersections when the number of points is odd:
C(n, 4) where n is the number of odd points on the circle
For instance, when n = 5, we have C(5,4) = 5
When n = 7, we have C(7,4) = 35
So, when n= 9, we have C(9,4) =126 points of intersection
BTW......
With 6 points, there are 13 points of intersection
By the "formula," 6 points should give us 15 points of intersection, but note that 3 diagonals actually meet in the center....thus...two "pair-wise" intersections are "lost"
And with 8 points, there are 47 points of intersection .... (if I counted correctly !!!)
