In the arithmetic sequence {an}, S9 = - 36, S13 = - 104, in the arithmetic sequence {BN}, B5 = A5, B7 = A7, then B6 = () A. ±42B. 42C. ±6D. 6 | Math enthusiast | Mathematical art

In the arithmetic sequence {an}, S9 = - 36, S13 = - 104, in the arithmetic sequence {BN}, B5 = A5, B7 = A7, then B6 = () A. ±42B. 42C. ±6D. 6

In ∵ arithmetic sequence {an}, S9 = 92 (a1 + A9) = 9A5 = - 36, S13 = 132 (a1 + A13) = 13a7 = - 104, in {BN} arithmetic sequence, B5 = A5 = - 4, B7 = A7 = - 8, ∵ B1 · Q4 = − 4b1 · Q6 = − 8, the solution is B1 = − 1, q = ± 2, ∵ B6 = B1 · Q5 = ± 42

In the arithmetic sequence {an}, S9 = - 36, S13 = - 104, in the arithmetic sequence {BN}, B5 = A5, B7 = A7, then B6 = ()
A. ±42B. 42C. ±6D. 6

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