数学机井29题有错误？

lyue2009

29. x/y>0?:

i x-y^2>0,

ii: y/x<0

解：
            

ià x > y^2 >=0 à
            不能确定y的正负性，甚至y可以等于0，所以不能够确定
            

iià y <>0 同时x,y异号àx/y < 0

答案：B

为啥这个题目选B？ x/y < 0  推不出 x/y>0呀？

sdtifa

since (2) tell us that y/x>0, it means that either x or y is negative. so you can answer the question is X/Y>0

ur answer will be no, x/y is not > 0. cuz  x/y is <0

[此贴子已经被作者于2009-2-24 9:25:10编辑过]

lyue2009

以下是引用sdtifa在2009-2-24 9:23:00的发言：

since (2) tell us that y/x>0, it means that either x or y is negative. so you can answer the question is X/Y>0

ur answer will be no, x/y is not > 0. cuz  x/y is <0

唉。。。没想到这个反证。。。谢啦~~~

45题也是同理吧。。。？