【答案】
分析:根據(jù)運(yùn)算順序先計(jì)算括號(hào)里的,第一個(gè)括號(hào)里的兩分母分解因式后,找出最簡(jiǎn)公分母進(jìn)行通分,然后利用同分母分式的減法法則:分母不變,只把分子相減;同時(shí)對(duì)第二個(gè)括號(hào)里的兩式進(jìn)行通分,利用同分母分式的加法法則計(jì)算后再把分子分解因式,然后利用除法法則,把除法化為乘法運(yùn)算,約分即可得到最簡(jiǎn)結(jié)果,最后把a(bǔ)與b的值代入,化簡(jiǎn)可得值.
解答:解:原式=(
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/0.png)
-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/1.png)
)÷(
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/2.png)
+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/3.png)
)
=(
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/4.png)
-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/5.png)
)÷
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/6.png)
=(
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/7.png)
-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/8.png)
)÷
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/9.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/10.png)
•
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/11.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/12.png)
•
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/13.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/14.png)
.
當(dāng)a=1+
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/15.png)
,b=1-
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/16.png)
時(shí),原式=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101191451198906116/SYS201311011914511989061016_DA/17.png)
=1.
點(diǎn)評(píng):此題考查了分式的化簡(jiǎn)求值,解答此類題時(shí),學(xué)生應(yīng)通觀全局,弄清運(yùn)算順序,分式的乘除法實(shí)質(zhì)是約分,對(duì)于分子分母是多項(xiàng)式的,要先將多項(xiàng)式分解因式,再約分,分式的加減法運(yùn)算關(guān)鍵是通分,通分的關(guān)鍵是確定各個(gè)分母的最簡(jiǎn)公分母,通常取各個(gè)分母所有因式的最高次冪的積作為最簡(jiǎn)公分母.學(xué)生做題時(shí)注意化簡(jiǎn)及求值的結(jié)果都必須為最簡(jiǎn).