Is anyway to prove this: <munderover> &#x220F;<!-- ∏ --> <mrow class="MJX-TeXAtom-ORD"

migongoniwt

migongoniwt

Answered question

2022-06-26

Is anyway to prove this: k = 1 n ( a k ) < ( 1 / n n ) ( k = 1 n ( 1 + a k a k + 1 ) ) n
ak and n are positive real number greater than 0.
EDIT: a_{k+1} becomes a_{1} when a_{k}=a_{n}, it is a cylic notation. SORRY.
Any ideas of how to attack the problem?? Thank You.
I don't know if this could help, but the 1/n is also the exponent for the left hand side. I'm thinking maybe of log??
I'm pretty sure that at some point it would be helpful the binominal coefficent?? I don't know.

Answer & Explanation

Christina Ward

Christina Ward

Beginner2022-06-27Added 19 answers

After the question get cleared up, the answer becomes a trivial application of GM AM. Since the a k are in cyclic notation. i.e. a n + 1 = a 1 , we have
k = 1 n a k = k = 1 n a k a k = a 1 ( k = 1 n 1 a k a k + 1 ) a n = k = 1 n a k a k + 1 a 1 = a n + 1  and rearrange  ( k = 1 n a k a k + 1 n ) n GM AM < ( k = 1 n 1 + a k a k + 1 n ) n = 1 n n ( k = 1 n 1 + a k a k + 1 ) n

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