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MathNet 2020 — Math Olympiad Vault — Part 04 Question 49

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 04

Question 49

Let $n \geq 3$ be an integer and let $1 \lt a_{1} \leq a_{2} \leq a_{3} \leq \cdots \leq a_{n}$ be $n$ real numbers such that $a_{1} + a_{2} + a_{3} + \cdots + a_{n} = 2n$. Prove that
$$
a_{1} a_{2} \cdots a_{n-1} + a_{1} a_{2} \cdots a_{n-2} + \cdots + a_{1} a_{2} + a_{1} + 2 \leq a_{1} a_{2} \cdots a_{n}
$$