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



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


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