MathDB
Inequality for geometric and arithmetic mean for n-1 numbers

Source: IMO ShortList 1991, Problem 26 (CZE 1)

August 15, 2008
Inequalityalgebrapolynomialn-variable inequalityIMO Shortlist

Problem Statement

Let n2,nN n \geq 2, n \in \mathbb{N} and let p,a1,a2,,an,b1,b2,,bnR p, a_1, a_2, \ldots, a_n, b_1, b_2, \ldots, b_n \in \mathbb{R} satisfying 12p1, \frac{1}{2} \leq p \leq 1, 0ai, 0 \leq a_i, 0bip, 0 \leq b_i \leq p, i \equal{} 1, \ldots, n, and \sum^n_{i\equal{}1} a_i \equal{} \sum^n_{i\equal{}1} b_i. Prove the inequality: \sum^n_{i\equal{}1} b_i \prod^n_{j \equal{} 1, j \neq i} a_j \leq \frac{p}{(n\minus{}1)^{n\minus{}1}}.