Sequence
2015-01-10 2:41 am
For a certain sequence, nth term = (n + 1)th term - 6. Sum of first 28 terms = 1624. Find the 1st term of the sequence.
回答 (2)
2015-01-10 5:25 am
✔ 最佳答案
nth term = (n + 1)th term - 6(n + 1)th term = nth term + 6
So the common difference = 6
Let a be the first term,
28/2[2a+(27)(6)]=1624
a=-23
So the ans is -23
2015-01-09 22:28:22 補充：
SOR, BELOW IS CORRECT
參考: ME1, ZZ
2015-01-10 5:32 am
For a certain sequence，nth term=(n+1)th term－6，Sum of first 28 terms=1624，
Find the 1st term of the sequence
Sol
a(n)=a(n－1)+6
d=6
a(16)=a(1)+15d=a(1)+90
1624=[a(1)+a(1)+90]*28/2
116=2a(1)+90
a(1)=13
Find the 1st term of the sequence
Sol
a(n)=a(n－1)+6
d=6
a(16)=a(1)+15d=a(1)+90
1624=[a(1)+a(1)+90]*28/2
116=2a(1)+90
a(1)=13
收錄日期: 2021-04-15 17:52:49
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https://hk.answers.yahoo.com/question/index?qid=20150109000051KK00078