MathDB
Chinese TST 2008 P6

Source:

April 3, 2008
inequalitiesgeometric sequencealgebra proposedalgebra

Problem Statement

Find the maximal constant M M, such that for arbitrary integer n3, n\geq 3, there exist two sequences of positive real number a1,a2,,an, a_{1},a_{2},\cdots,a_{n}, and b1,b2,,bn, b_{1},b_{2},\cdots,b_{n}, satisfying (1): \sum_{k \equal{} 1}^{n}b_{k} \equal{} 1,2b_{k}\geq b_{k \minus{} 1} \plus{} b_{k \plus{} 1},k \equal{} 2,3,\cdots,n \minus{} 1; (2): a_{k}^2\leq 1 \plus{} \sum_{i \equal{} 1}^{k}a_{i}b_{i},k \equal{} 1,2,3,\cdots,n, a_{n}\equiv M.