题目内容
下列等式一定成立的有( )A.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_ST/0.png)
B.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_ST/1.png)
C.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_ST/2.png)
D.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_ST/3.png)
【答案】分析:根据二次根式的性质对A、B、C、D四个选项进行一一计算判断;
解答:解:A、
=
=2,故A错误;
B、
=x2>0,故B正确;
C、∵b-
=b-
,∵b+1与0的关系不知道,故不能计算,故C错误;
D、当x<0时,
=-x3,故错误;
故选B.
点评:此题主要考查二次根式的性质和化简,计算时要仔细,是一道基础题.
解答:解:A、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/1.png)
B、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/2.png)
C、∵b-
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/3.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/4.png)
D、当x<0时,
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103195325227810327/SYS201311031953252278103004_DA/5.png)
故选B.
点评:此题主要考查二次根式的性质和化简,计算时要仔细,是一道基础题.
![](http://thumb2018.1010pic.com/images/loading.gif)
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