![](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>)
In the arithmetic sequence {an}, A4 = 7, a7 = 4, then A15 equals ()
a4 + 3d = a7
7 +3d = 4
d = -1
a15 = a7 + 8d
= 4 - 8
= -4
(D is tolerance)
The general formula of arithmetic sequence {an} is an = 14-3n
It is proved that when n ≥ 5, an
an14/3≈4.6666
Because n is an integer, n > = 5
The general term formula of an arithmetic sequence {an} is an = 3n-2, which is a formula for finding the sum of its first n terms
a1=1
a2=4
So d = 3
So Sn = n (3n-1) / 2
RELATED INFORMATIONS
- 1. It is known that the general term formula of arithmetic sequence {an} is | an | = 3n-5, and the sum formula of the first n terms is obtained We need to talk about it by category It is | an | = 16-3n
- 2. In the arithmetic sequence an, a16 + A17 + A18 = A8 = - 36, find TN = | A1 | + | A2 | + · + | an| The answer is TN = {- 3 / 2 times n square + 123 / 2n, (n is less than or equal to 21, n belongs to n *) 3 / 2 times n square - 123 / 2n + 1260 (n is more than 21, n belongs to n *)*
- 3. Given that the first term A1 of the arithmetic sequence {an} is less than 0, the tolerance D ≠ 0, and the absolute value A4 = the absolute value A12, if the first n terms and Sn get the minimum value, then n= I made a mistake!
- 4. It is known that the sum of the first n terms of the arithmetic sequence is Sn, and S13 < 0, S12 > 0, then the term with the smallest absolute value in the sequence is () A. Item 5 B. item 6 C. item 7 d. item 8
- 5. Let the sum of the first n terms of the sequence {an} be Sn = n ^ 2-8n. If TN is the sum of the first n terms of the sequence {an's absolute value}, find TN
- 6. In the arithmetic sequence {an}, A1 = - 60, A17 = - 12. (1) find the general term an, (2) find the sum of the first 30 terms of the sequence
- 7. Let the sum of the first n terms of the sequence {an} be SN. Given A1 = 1, Sn + 1 = 4An + 2, find: (1) let BN = an + 1-2an, prove that the sequence {BN} is an equal ratio sequence 2) Finding the general term of an The second answer is (1) bn＝a(n＋1)－2an＝3•2^(n－1) ∴[a(n＋1)]/[2^(n＋1)]－(an)/(2^n)=3/4 The sequence {(an) / (2 ^ n)} is an arithmetic sequence with 1 / 2 first term and 3 / 4 tolerance ∴(an)/(2^n)＝1/2＋(n－1)3/4＝3/4n－1/4 That is, an = (3n-1) & _; 2 ^ (n-2) (n ∈ n *) Question: how to get [a (n + 1)] / [2 ^ (n + 1)] - (an) / (2 ^ n) = 3 / 4 and why
- 8. Given the positive term sequence {an}, the first n terms and Sn satisfy 10sn = an2 + 5An + 6, and A1, A3, A15 are equal proportion sequence, find the general term an of the sequence {an}
- 9. An object with a mass of 1kg is subjected to two forces of 2n and 3N, Then the maximum and minimum accelerations of the object are -
- 10. If two hands push the same object with 3N at the same time, is the force on the object 3N or 6N? Same direction
- 11. Given that the sum of the first n terms of the sequence (an) is Sn = 2an-4n + 1, the general term formula of the sequence is obtained RT
- 12. The general term formula of known sequence (an) is an = 4N-1, Sn represents the sum of the first n terms of the sequence, and how much is S6 equal to?
- 13. The sum of the first n terms of the sequence an is Sn = 4N (square) - N + 2. Find the general term formula of the sequence an
- 14. It is known that the sum of the first n terms of the sequence an is Sn, and an + 2Sn = 4N (n ∈ n +). 1) to find the general term formula 2 of the sequence an It is known that the sum of the first n terms of an is Sn, and an + 2Sn = 4N (n ∈ n +) 1) The general term formula of the sequence an 2) If BN = Nan, find the first n terms of BN and TN
- 15. If the first n terms of the sequence {an} and Sn = 4n2-n + 2, then the general term formula of the sequence is an=______ ．
- 16. It is known that the general term formula of the sequence an is an = 2 ^ (5-N), and the general term formula of the sequence BN is BN = n + K. let CN = BN (anbn). In the sequence {CN}, if C5
- 17. If the solution set of inequality ax ^ 2-6x + A ^ 2 about X less than 0 is (1, m), then what is m?
- 18. Substitution of infinitesimal factors of higher number equivalence How do ^ 2 + (SiNx) ~ (sin2) / (SiNx) ~ (SiNx) ~ (sin2) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (sin2) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~ (SiNx) ~
- 19. Want to know how to prove the product of finite infinitesimal or infinitesimal
- 20. Finding limit limx-0 sin3x / sin5x