對于題目“化簡并求值:
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/0.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/1.png)
,其中a=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/2.png)
”,甲、乙兩人的解答不同.
甲的解答:
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/3.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/4.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/5.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/6.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/7.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/8.png)
-a=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/9.png)
-a=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/10.png)
;
乙的解答:
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/11.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/12.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/13.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/14.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/15.png)
+a-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/16.png)
=a=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_ST/17.png)
.
請你判斷誰的答案是錯(cuò)誤的,為什么?
【答案】
分析:因?yàn)閍=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/0.png)
時(shí),a-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/1.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/2.png)
-5=-4
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/3.png)
<0,所以
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/4.png)
≠a-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/5.png)
,故錯(cuò)誤的是乙.
解答:解:甲的解答:a=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/6.png)
時(shí),
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/7.png)
-a=5-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/8.png)
=4
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/9.png)
>0,所以
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/10.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/11.png)
-a,正確;
乙的解答:因?yàn)閍=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/12.png)
時(shí),a-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/13.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/14.png)
-5=-4
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/15.png)
<0,所以
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/16.png)
≠a-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/17.png)
,錯(cuò)誤;
因此,我們可以判斷乙的解答是錯(cuò)誤的.
點(diǎn)評:應(yīng)熟練掌握二次根式的性質(zhì):
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000036007496999/SYS201311030000360074969016_DA/18.png)
=-a(a≤0).
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對于題目:“化簡并求值,
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131103000428590612617/SYS201311030004285906126022_ST/0.png)
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