prep数学

kaneroy

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

yqhpsyche

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

yqhpsyche

错了，是T=1-1/2^k,选C

kaneroy

对啊，谢谢你啦

bobdog179

prep答案不是D吗？！仍然不会啊啊啊啊啊