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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
分析A选项
分析B选项
分析C选项
分析D选项
分析E选项
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（-a,b）(-b,a)在同一个象限，问（-x,y）是否也在这个象限？
xy>0;
ax>0
由于（-a,b）(-b,a)在同一个象限,所以ab>0,且这两点可能在第二或者第四象限内；
条件1.只能说明（-x,y）可能在第二象限，也可能在第四象限，所以不充分；
条件2. ax>0,明显不充分；
但是两个条件联立，可以发现当ax>0时，（-x,y）一定和（-a,b）(-b,a)在同一个象限内
XiaoningChan
(-a,b)和（-b,a）在同一象限时，两者横纵坐标的正负号一致，故ab＞0，-a与b异号，这两个坐标可能在第二或第四象限，故要想让（-x,y）与(-a,b)和（-b,a）在同一象限，除了要保证xy＞0，还要保证x与a同号。
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2022-09-25 21:37:09
兔小黄
ab>0这个是怎么推出来的，做题时完全没想到
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2022-07-09 02:37:06
leon小恶魔回复兔小黄
(-a, b) and (-b, a) are in the same quadrant of the xy-plane：那么-a和-b是同正或同负，a和b同正或同负，得出ab>0
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2022-11-26 18:44:23
leon小恶魔
由题目得出 ab＞0 联立(1) xy > 0 和 (2) ax > 0的条件的得出：ay＞0，再一步by＞0 ，那么x和a同正负，y和b同正负，那么（-x,y）和（-a,b）必定在同一象限
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2022-05-31 14:54:24
1229394ifpm
题目 两个点 同一个 象限------ a，b 同号 同正同负 所以可以确定不是第二就是第四。 条件一， 得出 xy 这个点不是第二就是第四 无法确定 条件二， ax大于零得出 a x 同号 但是不知道y 所以不行。 1+2 xy 在第二第四象限 而且 x 和 a （b）同号 所以 充分
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2021-06-08 09:41:42
Litchichi
主要就是确认 a, b, x, y 的正负号，因为在题干中已经给出 a, b 的关系，因此，在确认（-x, y） 是否与 (-a, b)及(-b, a)在同一象限，则需要确认 x, y 的正负号与 a, b 的正负号的关系，才可能确认结果，而无论是条件1或条件2，单独来看，均无法实现 x, y, a的正负号关系，所以，只能选 C，可加上题干给出的 a 和 b 的正负号关系，再加上两个条件给出的 x, y, 和 a 的正负号关系，就能推出结果。
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2020-12-12 19:47:56
catontheroof
https://www.manhattanprep.com/gmat/forums/if-ab-does-not-equal-zero-t2975.html
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2019-05-16 17:00:45
Kath1230
头好晕看这道题
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2019-02-10 17:53:49
月冷隐回复Kath1230
你考了吗？在很多解析里都看到你留言，哈哈。
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2019-05-23 04:49:52
拽mat
注意CD的区别
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2018-04-01 18:59:23
OoO
审题啊 问题是is point (-x, y) in this same quadrant? 注意限定词this 则一定要判断（-x,y)在一个确定的象限且和（-a,b),(-b,a)一致 而不是只判断它在同一个象限
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2016-10-30 12:02:02
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