(a^2-9)/(a^2-4a+3)×（a-1)/a^2+4a+3
问题描述：
(a^2-9)/(a^2-4a+3)×（a-1)/a^2+4a+3
(2a^2-3a+1)/（1-a^2)÷(4a^2-4a+1)/(2a^2+a-1)
(3x+9)/(4-4x+x^2)÷（x+3）/(x-2)
答
(a^2-9)/(a^2-4a+3)×（a-1)/a^2+4a+3
=[(a-3)(a+3)/(a-3)(a-1)×(a-1)/[(a+3)(a+1)]
=(a+3)/(a-1)×(a-1)/[(a+3)(a+1)]
=1/(a+1)