![](data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 72 71" width="72"></svg>)
If Sn = 2N-1, then A8=______ ．
Because the sum of the first n terms of the sequence {an} is Sn, if Sn = 2N-1, then A8 = s8-s7 = 28-1 - (27-1) = 27 = 128
Let the first n terms of sequence {an} and Sn = N2, then A8=______ ．
∵ an = sn-sn-1 (n ≥ 2), Sn = N2 ∵ A8 = s8-s7 = 64-49 = 15, so the answer is 15
Given that the sum of the first n terms of the sequence {an} is Sn = N3, then A6 + A7 + A8 + A9 equals ()
A. 729B. 387C. 604D. 854
From the meaning of the title, we can get A6 + A7 + A8 + A9 = s9-s5 = 93-53 = 604, so we choose C
RELATED INFORMATIONS
- 1. Given that the sum of the first n terms of a sequence an is Sn, and an = 3 ^ n + 2n, then SN is equal to
- 2. Given that the first n terms of an and Sn are equal to the square of n minus n plus 1, the general term formula of an is obtained
- 3. Let the first n terms and Sn = (- 1) ^ n (2n ^ 2 + 4N + 1) - 1 of sequence {an} 1, find the general term formula an of sequence {an} 2, record BN = (- 1) ^ n / an, find the first n terms and TN of the sequence {BN}
- 4. Given that the general term formula of sequence is an = 2n-47, then when Sn takes the minimum value, n=______ ．
- 5. Final warm-up (2) 17 questions, the first N-term sum of sequence {an} is Sn, known A1 = 1. An + 1 = (n + 2) Sn / N (n ∈ n *) It is proved that: (1) the equal ratio sequence of sequence {Sn / N}. (2) Sn + 1 = 4An focuses on the second question,
- 6. Sequence {an} satisfies A1 = 1 / 2, a1 + A2 +.. + an = n square an, find an
- 7. The first n terms of known sequence {an} and Sn = 1-5 + 9-13 + 17-21 +... + (- 1) ＾ n * (4n-3) Find S15 + s22-s31
- 8. Given the sum of the first n terms of the sequence {an} and Sn = - n ^ 2 + 4N 1) find the general term formula of an; 2) find the sum of the first n terms of the sequence {9-2an / 2 ^ n} Because the original problem is the quadratic of negative n, not the quadratic of negative n, so ~ A1 seems to be 3, not 5! The general formula is also wrong!
- 9. It is known that the sum of the first n terms of two arithmetic sequences {an}, {BN} is Sn and TN respectively. If Sn / TN = (5N + 3) / (2n-1), then A9 / B9 is obtained Such as the title
- 10. If Sn / TN = (2n + 3) / (3n-1), calculate A9 / B9
- 11. Let an be an equal ratio sequence composed of positive numbers. If the sum of the first n terms is known as a2a4 = |, S3 = 7, then S5 = |?
- 12. The {an} is an equal ratio sequence composed of positive numbers, Sn is the sum of the first n terms, a2a4 = 1, S3 = 7, S5 =?
- 13. It is known that SN is the sum of the first n terms of the equal ratio sequence {an}, and S3, S9 and S6 are equal difference sequence A .A3+A6=A9 B.A3*A6=A9 C.A3+A6=2A9 D.A3*A6=A9^2 Ask for detailed explanation
- 14. It is known that the sum of the first n terms of the equal ratio sequence {an} is Sn, A4 equals 2A3, S2 equals 6. Find the general term formula of the sequence {an}
- 15. Let the sequence {an} be an equal ratio sequence, the sum of the first n terms is Sn, and S3 = 3a3, and find the value of the common ratio Q As above
- 16. If an = BN, find n
- 17. The first term of the infinite arithmetic sequence {an} is A1 = 93, and the tolerance D1 = - 7. The first term of the infinite arithmetic sequence {BN} is B1 = 17, and the tolerance D2 = 12, Then, how many items are there in these two sequences with equal values?
- 18. Let A1 and d be real numbers, the first term be A1, the sum of the first n terms of the arithmetic sequence {an} with tolerance d be Sn, satisfying s5s6 + 15 = 0, then the value range of D is______ ．
- 19. Let {an} be an arithmetic sequence with the first term of 3 and the tolerance of D, and {BN} be a sequence determined by BN = an + an + 1, then what are the first n terms of {BN} and Sn?
- 20. The known sequence an satisfies: an + 1-2an = 2 ^ n + 1, and A1 = 2 (1). It is proved that {an / 2 ^ n} is the key to find the sequence an of arithmetic sequence (2)