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标题: GWD 5-8 [打印本页]

作者: xianwharton 时间: 2005-12-26 07:13 标题: GWD 5-8

Q8:

The infinite sequence a₁, a₂,…, a_n,… is such that a₁ = 2, a₂ = -3, a₃ = 5, a₄ = -1, and a_n = a_n-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:

作者: leadership 时间: 2005-12-26 19:45

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

作者: xianwharton 时间: 2005-12-26 20:50

thanks !!!!

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