30. v(u+v)≠0,v>0(不是很记得),问1/(u+v)>1/u+v? MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
1) u+v>0 MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
2) u>0 MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
Key:MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
我选c 用1/(u+v)-1/u-v>0求值,最后是u(u+v)和[v+u(u+v)]同号,所以1和2合起来是可以的;把问题的不等式拿去通分就可以了MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
比较左边的和右边的谁大,左边-右边是>0还是<0就可以了,你在纸上画画,就出来了。分子分母同号大于0,异号小于0,两个条件合在一起刚好同号,原题还有一个条件是v>0MingLiU","serif"; mso-bidi-font-family: PMingLiU; mso-font-kerning: 0pt;">
有讨论贴拉。。我们都去wuyusiyu mm的帖子讨论
另外,这个题目选B。。
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