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题库 / Prep2007E2-DS-65
If ab ≠ 0 and points (-a, b) and (-b, a) are in the same quadrant of the xy-plane, is point (-x, y) in this same quadrant?
(1) xy > 0
(2) ax > 0
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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题目：ab≠ 0 --> a≠ 0 ，b≠ 0 ；(-a, b) and (-b, a) 同象限-->ab同号。问(-x, y) 是否同象限-->xy什么符号？
(1)xy > 0 --> xy同符号。但是不知道具体什么符号，insufficient
(2)ax > 0 --> ax同符号~abx同号。但是不知道y什么符号，insufficent
(1)+(2) abxy同符号 --> 可以判断是否同象限，sufficient
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