The sum of the first n terms of a sequence is 2n^2+n
(a) find the nth term of the sequence.
(b) Show that it is an arithmetic sequence. Hence, find the common difference.
步驟+答案, 謝謝!!
F.6 Maths. Sequences & Series
2013-11-30 5:06 am
回答 (3)
2013-11-30 7:16 am
✔ 最佳答案
T1 + T2 + ........ + Tn = 2n² + n= (2n+1)(n)
=2 (2n+1)(n)/2
=(4n+2)(n)/2
=(4n-4+4+2)(n)/2
=[4(n-1)+6](n)/2
=[2(3)+(n-1)4](n)/2
a = 3; d = 4
nth term = a + (n-1)d = 3+(n-1)4
= 3 + 4n - 4 = 4n - 1
2013-12-07 5:07 am
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伂剪亵咑優哟
伂剪亵咑優哟
2013-11-30 7:42 am
另有一個好方法~
T(n) = S(n) - S(n-1)
T(n) = S(n) - S(n-1)
收錄日期: 2021-04-27 20:37:49
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20131129000051KK00149