prep数学

thumbbunny · 发表于 2012-5-13 01:11:09

For every integer k from 1 to 10, inclusive, the kth term of a certain sequence is given by （-1）^k+1 *1/2^k (-1的k+1次方乘以2的k次方分之一). If T is the sum of the first 10 terms in the sequence, then T is

(A) greater than 2
(B) between 1 and 2
(C) between 1/2 and 1
(D) between 1/4 and 1/2
(E) between 1/4

题目的意思我明白，就是不会算法，要死算吗？那不是要算死了

sally77589 · 发表于 2012-5-13 08:39:39

不是啊，最后可以得出一个首项是1/2，Q是1/2的等比数列，得出T=1+1/2^k

sally77589 · 发表于 2012-5-13 10:37:11

错了，是T=1-1/2^k,选C

thumbbunny · 发表于 2012-5-14 10:12:45

错了，是T=1-1/2^k,选C

-- by 会员 sally77589 (2012/5/13 10:37:11)

啊啊啊啊，对啊，谢谢你啦

增小熊 · 发表于 2012-8-26 22:08:47

prep答案不是D吗？！仍然不会啊啊啊啊啊

错了，是T=1-1/2^k,选C

-- by 会员 sally77589 (2012/5/13 10:37:11)

啊啊啊啊，对啊，谢谢你啦

-- by 会员 thumbbunny (2012/5/14 10:12:45)

prep数学

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