上2题约分,后题通分,

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上2题约分,后题通分,上2题约分,后题通分, 上2题约分,后题通分,(3)(a^2-2a+1)/(1-a^2)=(a-1)^2/(1+a)(1-a)=-(a-1)/(a+1)(4)(4a-a

上2题约分,后题通分,
上2题约分,后题通分,
 

上2题约分,后题通分,
(3)
(a^2-2a+1)/(1-a^2)
=(a-1)^2/(1+a)(1-a)
=-(a-1)/(a+1)
(4)
(4a-a^2-4)/(4-a^2)
=-(a-2)^2/(2+a)(2-a)
=(a-2)/(a+2)
9.
(1)
最简公分母是12a^2b^2c
a/2b^2=6a^3c/12a^2b^2c
-c/3ab=-4abc^2/12a^2b^2c
b/4a^2c=3b^3/12a^2b^2c
(2)
最简公分母是a+b
a-b=(a+b)(a-b)/(a+b)
b/(a+b)
(3)
最简公分母是(a+1)^2(a-1)
(a-1)/(a^2+2a+1)=(a-1)^2/(a+1)^2(a-1)
3/(1-a^2)=-3(a+1)/(a+1)^2(a-1)
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