congruent pairs of lines = 2012 more than not congruent
Source: China Northern MO 2012 p4 CNMO
May 4, 2024
combinatoricscombinatorial geometrygeometry
Problem Statement
There are () straight lines on the plane. For two straight lines and , if there are at least two straight lines among the remaining lines that intersect both straight lines and , then and are called a congruent pair of staight lines, otherwise it is called a separated pair of straight lines. If the number of congruent pairs of straight line among straight lines is more than the number of separated pairs of straight line , find the smallest possible value of (the order of the two straight lines in a pair is not counted).