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题库 / Prep2007E1-DS-125
The sequence a1, a2, a3, . . . , an of n integers is such that ak = k if k is odd and ak = -ak - 1 if k is even. Is the sum of the terms in the sequence positive?
(1) n is odd.
(2) an is positive.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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Is the sum of the terms in the sequence 【positive】
不需要知道具体的数值...
做数学的时候老是被鬼打墙！！！！我瞎了！！！
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