a的平方-1分之2a+1乘以a的平方-a分之a的平方-2a+1减去a+1分之1,其中a=-二分之一 化简求值

(2a+1)/(a²-1)×[(a²-2a+1)/(a²-a)]-1/(a+1)
=(2a+1)/(a-1)(a+1)×[(a-1)²/a(a-1)]-1/(a+1)
=(2a+1)/[a(a+1)]-a/[a(a+1)]
=(a+1)/[a(a+1)]
=1/a
=1/(1/2)
=2