1.
i) If 7 points of 12 are in a straight line, then find the number of traingles that can be formed by selecting any 3 of them
ii)Under the same situation , find the number of straight lines that can be formed by jining these lines
1. A triangle is formed by joining any three points which are not collinear
in first part no. of triangles formed = no. of triangle formed by 12 points-no. of triangles formed by 7 points
=12C3-7C3
=220-35=185
2.A straight line is formed by joining any two points
no. og straight lines=straight lines formed by 12 poins-straight lines formed by 7 points+1 (1 is added because the 7 points which are on a straight line also represent a straight line)
so no. of lines=12C2-7C2+1
=66-21+1=46