In the arithmetic sequence {an}, Sn is the sum of the first n terms of {an}, A1 = 25, S17 = S9, find the maximum value of Sn
s9=s17
It can be seen that A10 + a11 + A12 + A13 + A14 + A15 + a16 + A17 = 0
It is known that A13 = - A14
Because A1 = 25 > 0
So it's a decreasing sequence, A13 > 0, A14
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