题目内容
如果a是非零实数,则下列各式中一定有意义的是( )A.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_ST/0.png)
B.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_ST/1.png)
C.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_ST/2.png)
D.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_ST/3.png)
【答案】分析:利用二次根式有意义的条件:被开方数是非负数即可作出判断.
解答:解:A、当a<0时,
无意义,故选项错误;
B、当a>0时,-a<0,则2
无意义,故选项错误;
C、a≠0,则-a2<0,则
无意义,故选项错误;
D、a≠0,则
≥0,则
一定有意义,故选项正确.
故选D.
点评:本题考查了二次根式的有意义的条件:二次根式中的被开方数必须是非负数,否则二次根式无意义.
解答:解:A、当a<0时,
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_DA/0.png)
B、当a>0时,-a<0,则2
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_DA/1.png)
C、a≠0,则-a2<0,则
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_DA/2.png)
D、a≠0,则
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_DA/3.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131022164720061686481/SYS201310221647200616864004_DA/4.png)
故选D.
点评:本题考查了二次根式的有意义的条件:二次根式中的被开方数必须是非负数,否则二次根式无意义.
![](http://thumb2018.1010pic.com/images/loading.gif)
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