# Find the number of intersection points?(Combinatorics)

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• April 30th 2009, 05:43 AM
fardeen_gen
Find the number of intersection points?(Combinatorics)
If you draw $m$ straight lines in the plane consisting of $x_{1}$ parallel in one direction, $x_{2}$ parallel in different direction ... and $x_{n}$ parallel in another direction and no three of the lines meeting at a point, show that the number of intersection points is $\sum_{i