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Q8:
The infinite sequence a1, a2,…, an,… is such that a1 = 2, a2 = -3, a3 = 5, a4 = -1, and an = an-4 for n > 4. What is the sum of the first 97 terms of the sequence?
A. 72
B. 74
C. 75
D. 78
E. 80
Answer:
leadership 当前离线
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an的值是循环的,每四个的和为2-3+5-1=3
97=4*24+1,所以前97项的和为24*3+2=74,选B
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