For the sum of the first n terms of an arithmetic sequence is 2n2. Find the 2nd term of the sequence.
a. 6
b. 12
c. 20
d. 24
arithmetic sequence
2011-03-13 1:53 am
回答 (3)
2011-03-13 2:14 am
✔ 最佳答案
Sum of the first n terms of an arithmetic sequence is 2n2(n/2)[2a + (n - 1)d] = 2n^2
2a + (n - 1)d = 4n
Sub. n = 1, a = 2.
Since a + (n - 1)d = 4n - a
Sub. a = 2, n = 2, the 2nd term of the sequence is 6 (A)
2011-03-13 3:55 am
S1 = 2(1^2) = 2
S2 = 2(2^2) = 8
2nd term = S2 - S1 = 8 - 2 = 6
S2 = 2(2^2) = 8
2nd term = S2 - S1 = 8 - 2 = 6
2011-03-13 3:07 am
收錄日期: 2021-04-23 23:23:34
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