a-b=2ab
ab=(a-b)/2
分式2a+ab+2b/a-3ab+b
=(2a+(a-b)/2+2b)/(a-3(a-b)/2+b)
=1/2(4a+a-b+4b)/(1/2(2a-3(a-b)+2b))
=(5a+3b)/(-a+5b)化简分式a^2-4/a^2-4a+3*[(a-3)/a^2+3a+2]化简分式a^2-4/a^2-4a+3*[(a-3)/a^2+3a+2]=(a+2)(a-2)/(a-3)(a-1)*[(a-3)/(a+2)(a+1)]=(a-2)/(a-1)(a+1)=(a-2)/(a^2-1)