Problem

Source: Iran TST 2007, Day 3

Tags: combinatorics proposed, combinatorics



Suppose $n$ lines in plane are such that no two are parallel and no three are concurrent. For each two lines their angle is a real number in $[0,\frac{\pi}2]$. Find the largest value of the sum of the $\binom n2$ angles between line. By Aliakbar Daemi