通分 1.a/(a^2-9),a-1/a^2+6a+9 2.x/2(x+1),1/x^2-x 3.1/x^2-4,x/4-2x

通分 1、a/(a^2-9)和(a-1)/a^2+6a+9,a/(a^2-9)=a/(a+3)(a-3),(a-1)(/a^2+6a+9) =(a-1)/(a+3)^2(a+3)=(a-1)/(a+3)(a+3),公分母 (a+3)(a+3)(a-3),即a/(a^2-9)=a/(a+3)(a-3)= a(a+3)/(a+3)(a+3)(a-3),(a-1)(/a^2+6a+9) ...