Monday, 9 January 2017

inequality - If a1,a2,...,an are n positive real numbers such that a1.a2....an=1, then show that (1+a1).(1+a2)...(1+an)ge2n

My attempt:



Using Arithmetic Mean Geometric Mean for a1,a2,...,an,
a1+a2+...+annna1.a2....an
a1+a2+...+ann



Therefore, (1+a1)+(1+a2)+...+(1+an)n=(1+1+...ntimes)+(a1+a2+...+an)n=n+(a1+a2+...+an)nn+nn



Or simply, (1+a1)+(1+a2)+...+(1+an)n2




Now, Using Arithmetic Mean Geometric Mean for (1+a1),(1+a2),...,(1+an),
(1+a1)+(1+a2)+...+(1+an)nn(1+a1).(1+a2)....(1+an)



But, (1+a1)+(1+a2)+...+(1+an)nn(1+a1).(1+a2)....(1+an)and(1+a1)+(1+a2)+...+(1+an)n2
don't necessarily imply that n(1+a1).(1+a2)....(1+an)2



This is where I require help to proceed further.

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