It is known that the real number sequence an is equal ratio sequence and the common ratio is Q It is known that the real number sequence a (n) is an equal ratio sequence and the common ratio is Q. for all positive integers n > 1, there is: ((a (n + 1)) (s (n-1)) + (a (n-1)) (s (n + 1))) / 2

Let a (n) = A1 * q ^ (n-1), then s (n) = A1 (1-Q ^ n) / (1-Q)
A (n + 1), s (n + 1) and substitute them into the original inequality
Q ^ (n-2) * (1-Q) 0. So Q ^ (n-2) * (1-Q) > 0
That is, when q = 0
2. When Q > 0, for any n: Q ^ (n-2) > 0, so Q ^ (n-2) * (1-Q)

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