There are 50 lines in a plane, no two of them are parallel, no three of them meet at the same point, and no three points of intersections are collinear.
Let denote the number points of intersection, and denote the number of new lines formed by joining the points of intersection.
Find .
Clarification: A line can be formed by joining two points(created by the intersection of lines). A line so formed qualifies to be 'new' line if it does not lie on the pre-existing lines.
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Since no two lines are parallel every line intersects every other line, which means the number of points created is A = ( 2 5 0 ) = 1 2 2 5 .
The total number of lines which can be created by ′ A ′ points are ( 2 ( 2 5 0 ) ) .
But this doesn't give us the number of new lines created because some of the lines created by joining the new points lie on the existing lines. We need to subtract the unwanted ones. Observe that there will be 50 sets of 49 co-linear points. Thus number of new lines created are
B = ( 2 ( 2 5 0 ) ) − 5 0 × ( 2 4 9 ) = 6 9 0 9 0 0
Thus A + B = 6 9 2 1 2 5 .