初二的分式题目4个【急】

2(1-x)^2=2[-1*(x-1)]^2=2*(-1)^2(x-1)2=2(x-1)^2
所以最简公分母是2(x-1)^3

12/(a^2-9)+2/(a+3)
=12/(a^2-9)+2(a-3)/(a+3)9a-3)
=12/(a^2-9)+(2a-6)/(a^2-9)
=(12+2a-6)/(a^2-9)
=(2a+6)/(a^2-9)
=2(a+3)/(a+3)(a-3)
=2/(a-3)

a/b-b/a-(a^2+b^2)/ab
=a^2/ab-b^2/ab-(a^2+b^2)/ab
=(a^2-b^2-a^2-b^2)/ab
=-2b^2/ab
=-2b/a

已知ab=1
则a/(a+1)+b/(b+1)
=[a(b+1)+b(a+1)]/(a+1)(b+1)
=(ab+a+ab+b)/(ab+a+b+1)
=(1+a+1+b)/(1+a+b+1)
=1

(x-1)^3 (1-x)^3

12/(a+3)(a-3)+2/(a+3)=(12+2a-6)/(a+3)(a-3)
=2(a+3)/(a+3)(a-3)=2/a-3

题没表示清楚理解不同答案不同
a^2-b^2