a 1 a 1 2 + 4 + a 2 a 2 2 + 4 + ⋯ + a n a n 2 + 4 ≥ 2 0 1 7
Find the least positive integer value of n such that for any n positive reals a 1 , a 2 , … , a n , the inequality above is satisfied.
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Simplifying the expression ( a 1 + a 2 + a 3 + . . . . . . . . + a n ) + 4 ( a ! 1 + a 2 1 + a 3 1 + . . . . . . . + a n 1 ) ≥ 2 0 1 7 = > ∑ i = 1 n ( a i + a i 4 ) ≥ 2 0 1 7
Now applying A.M.-G.M. a i + a i 4 ≥ 2 a i × a i 4 = 4
We will find the minimum value of n .The n will minimum when it will holds the equality.So each a i + a i 4 will be 4
So, putting this value ∑ i = 1 n 4 ≥ 2 0 1 7 ⟹ 4 n ≥ 2 0 1 7 ⟹ n ≥ 2 0 1 7 / 4 = 5 0 4 . 2 5
The next integer n = 5 0 5 will be the minimum value.