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Prove that the product is not less than 2^n

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September 24, 2010
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Problem Statement

Given nn positive real numbers a1,a2,,ana_1, a_2, \ldots , a_n such that a1a2an=1a_1a_2 \cdots a_n = 1, prove that (1+a1)(1+a2)(1+an)2n.(1 + a_1)(1 + a_2) \cdots (1 + a_n) \geq 2^n.