(a²-9)/(a+1)=0
a²-9=0
a=3或a=-3
(a-1)/(a²-4a+4)/[(a²-1)/(a²-4)]
[(a-1)/(a-2)²][(a+2)(a-2)/(a+1)(a-1)]
=(a+2)/[(a-2)(a+1)]
当a=3时,原式=5/4
当a=-3时,原式=1/10