The problem:
N points are given on a 2-dimensional plane. What is the maximum number of points on the same straight line?
The problem has O(N2<
It is unlikely for a $o(n^2)$ algorithm to exist, since the problem (of even checking if 3 points in R^2 are collinear) is 3Sum-hard (http://en.wikipedia.org/wiki/3SUM)