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The known sequence {an} satisfies A1, A2-A3, a4-a3 , an-a (n-1) is the expression of finding an from the equal ratio sequence (1) with Prime Minister of 1 and common ratio of 1 / 3 (2) If BN = (2n-1) an, find the first n terms and Sn of the sequence {BN} It's wrong. (1) it should be A1, a2-a1, a3-a2 ，
You have entered the wrong topic. The first few items should be wrong,
1. Add up A1, a2-a1,. An-a (n-1) to get the expression, and then there is only an left, which is just the sum of the first n terms of the known equal ratio sequence. Simplify it to get an = 3 / 2 - (1 / 2) * (1 / 3) ^ n-1;
The expression of BN is an arithmetic sequence + an arithmetic sequence + a arithmetic sequence (the expression of an is the product of an arithmetic sequence and an arithmetic sequence, such as n * (1 / 3) ^ n), Let's talk about how to find the difference sequence: add SN to an with A1, and then multiply Sn by the common ratio Q of the equal ratio sequence in the difference sequence to get Q * Sn, and then use Q * Sn Sn SN. The expression is very regular. After sorting out, we can get a simple one variable linear equation about Sn and solve it
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