aa<1时,化简(a²-2a+1)/(a²-1)
a(a²-2a+1)/(a²-1)=(a-1)²/(a-1)(a+1)=1/(a+1)因为a<1,所以(a-1)²>1,(a+1)无论结果怎样,原式=1/a+1.