The number of points of intersection of
37 straight lines is 37C2, but 13 of them pass through the point A.
Therefore instead of getting 13C2 points we get merely one point.
Similary, 11 straight lines out of the given 37 straight lines intersect at B. Therefore instead of getting 11C2 points, we get only one point.
Hence, the number of intersection points of the lines is
= 37C2− 13C2− 11C2+2