a的平方-9/a的平方+6a+9除法a-3/a的平方+a-a的平方/a-1 =(a^2-9)/(a^2+6a+9)÷[(a-3)/(a^2+a)]-a^2/(a-1)=(a+3)(a-3)/(a+3)^2*a(a+1)/(a-3)-a^2/(a-1)=a(a+1)/(a+3)-a^2/(a-1)=[a(a+1)(a-1)-a^2*(a+3)]/[(a+3)(a-1)]...