The sum of the first n terms of sequence an is Sn A1 = 1 for any n > = 2 3sn-4 an 2-3s (n-1) / 2 General term formula for calculating the value of A2 A3 by assembly arithmetic sequence

3sn-4 + 2-3s (n-1) / 2 = 2 * ansn-sn-1 = an, 3 / 2S (n-1) + an = 2 - (1) A2 = 2 - 3 / 2S1 = 1 / 2. Similarly, A3 = - 1 / 4 (1) can be written as Sn + 1 / 2S (n-1) = 2 times (- 1 / 2) to get (- 1 / 2) (s (n-1) + 1 / 2S (n-2)) = 2 * (- 1 / 2) summation

Let {an} be an equal ratio sequence, Sn be the sum of the first n terms, A2 * A3 = 2A1, and the median of the equivalences of A4 and 2a7 is 5-4, so find S5

Then a2a3 = a1a4
So a1a4 = 2A1
So A4 = 2
The mean difference between A4 and 2a7 is 5 / 4
2×5/4=a4+2a7
So A7 = 1 / 4
So Q & # 179; = A7 / A4 = 1 / 8
q=1/2
So A1 = A4 / Q & # 179; = 16
So S5 = A1 * (1-Q ^ 5) / (1-Q) = 31

RELATED INFORMATIONS

1. It is known that {an} is an equal ratio sequence, and Sn is the sum of its first n terms. If A2 * A3 = 2A1, and the median of the difference between A4 and 2a7 is 5 / 4, then S5=
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