Let Sn be the sum of the first n terms of the arithmetic sequence {an}, A12 = - 8, S9 = - 9, then S16=______ ．

Let Sn be the sum of the first n terms of the arithmetic sequence {an}, A12 = - 8, S9 = - 9, then S16=______ ．

If S9 = 12 (a1 + A9) × 9 = - 9, and a1 + A9 = 2a5, we can get, A5 = - 1. From the properties of arithmetic sequence, we can get, a1 + a16 = A5 + A12, then S16 = 12 (a1 + a16) × 16 = 12 (A5 + A12) × 16 = - 72

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