In a plane there are n lines, no two lines of which are parallel and no three of which are concurrent. how many triangles can be formed with their points of interaction as vertices ?
[m=nc2]
1) mc2 - n*nc3
2) mc3 - n*(n-1)c2
3) mc3 - n*(n-1)c3
4) mc2 - (n-1)*nc2