how many (i) straight lines (ii) triangle can be formed by joining 12 points, 7 of which are in the same line.
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3 points needed to form a triange. Total possibilities is 12C3. However, 7 points are in the same line (collinear), hence we can't have a traingle.
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Answer:
straight lines=12 points
¹²C2=66
no. of straight lines using collinear
⅞
7C2 =28
req lines 66-28+1 =39
triangles
¹²C3=220
7C3=35
req 220-35=185
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