Problem

Source: 2015 Saudi Arabia IMO TST II p3

Tags: inequalities, algebra, n-variable inequality



Let a1,a2,...,an be positive real numbers such that a1+a2+...+an=a21+a22+...+a2nProve that 1i<jnaiaj(1aiaj)0Võ Quốc Bá Cẩn.