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2024 BxMO P1

Source: 2024 BxMO P1

April 27, 2024
Algebra inequalitySequencesalgebrainequalities

Problem Statement

Let a0,a1,,a2024a_0,a_1,\dots,a_{2024} be real numbers such that ai+1ai1\left|a_{i+1}-a_i\right| \le 1 for i=0,1,,2023i=0,1,\dots,2023. a) Find the minimum possible value of a0a1+a1a2++a2023a2024a_0a_1+a_1a_2+\dots+a_{2023}a_{2024} b) Does there exist a real number CC such that a0a1a1a2+a2a3a3a4++a2022a2023a2023a2024Ca_0a_1-a_1a_2+a_2a_3-a_3a_4+\dots+a_{2022}a_{2023}-a_{2023}a_{2024} \ge C for all real numbers a0,a1,,a2024a_0,a_1,\dots,a_2024 such that ai+1ai1\left|a_{i+1}-a_i\right| \le 1 for i=0,1,,2023i=0,1,\dots,2023.