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题库 / Prep2007E1-DS-152
If xyz > 0, is x > 0 ?
(1) xy > 0
(2) xz > 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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xy > 0 both are positive or both negative
xz > 0 both are positive or both negative
if x < 0 then z < 0 and y < 0 but xyz < 0 so this doesn't work
if x > 0 then y > 0 and z > 0 and xyz > 0 so this works and x > 0
同样的，列出xyz > 0的所有x,y,z的正负组合，再用(1) (2)分别去筛，(1) (2)都不能使结果唯一的话，对剩下的结果查重，看二者的交集是否能使结果唯一。
我吐了，这道题都做错了