(1)(a^2-1)/(a^2-a-2)约分
=(a+1)(a-1)/(a-2)(a+1)
=(a-1)/(a-2)
(2)x(x^2+x)/x^2(x^2-1)约分
=x²(x+1)/x²(x+1)(x-1)
=1/(x-1)很容易噢!