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题库 / Prep2007E1-PS-37
For every integer k from 1 to 10, inclusive, the kth term of a certain sequence is given by ~$\left ( -1 \right )^{k+1}\left ( \frac{1}{2^{k}} \right )$~. If T is the sum of the first 10 terms in the sequence, then T is
greater than 2
between 1 and 2
between ~$\frac{1}{2}$~ and 1
between ~$\frac{1}{4}$~ and ~$\frac{1}{2}$~
less than ~$\frac{1}{4}$~
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笔记：这个题竟然没看出来等比数列，绝了。
Sn=a1*(1-q^n)/(1-q)（q≠1)
公比是-1/2
a1=1/2
求和
2^10=1024
算完等于1023/1024 *1/3
近似于1/3
1/3在1/4和1/2之间选D
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