The number of straight lines that can be drawn through n non collinear points is ____
nC2
To form a straight line, we need 2 distinct points. If there are ,say, 3 or more points that are collinear, we can draw only 1 line through it.
From this, we infer that of there are n non collinear points, then every 2 points will make up a straight line and hence the number of straight lines formed is nothing but number of ways of selecting 2 points from n points = nC2