MathDB
Sixth Problem

Source: Last round of the Bulgarian Mathematical Olympiad 2009 Maybe Hard

June 22, 2009
integrationcalculusderivativeinequalities proposedinequalities

Problem Statement

Prove that if a1,a2,,an a_{1},a_{2},\ldots,a_{n}, b1,b2,,bn b_{1},b_{2},\ldots,b_{n} are arbitrary taken real numbers and c1,c2,,cn c_{1},c_{2},\ldots,c_{n} are positive real numbers, than \left(\sum_{i,j \equal{} 1}^{n}\frac {a_{i}a_{j}}{c_{i} \plus{} c_{j}}\right)\left(\sum_{i,j \equal{} 1}^{n}\frac {b_{i}b_{j}}{c_{i} \plus{} c_{j}}\right)\ge \left(\sum_{i,j \equal{} 1}^{n}\frac {a_{i}b_{j}}{c_{i} \plus{} c_{j}}\right)^{2}.