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It is known that the sum of the first n terms of sequence an is Sn, and the point (an, Sn) (n ∈ n) is on the image of function y = 18-2x 1 find the formula of sequence an Let BN = lgan, try to judge whether BN is equal difference sequence or equal ratio sequence, and prove your conclusion 3 find the n value of the first n terms and the maximum value of the sequence BN in 2
A = s-sn-1 according to the meaning of Sn = 18-2an, we can get 2An = 18-sn (1). Similarly, we can get 2A = 18-s (2) n-1 n-1 (1) - 2 a = 18-s - (18-s) n n-1 n n-1. We can get 2a-2a = S-S = - an n-1 n n-1 n, that is, 2a-2a = - an n-1 n, so 3A = 2An n n-1, we can know that an is an equal ratio
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