a²-1/a²-2a+1=（a-1）（a+1）/（a-1）²=（a+1）/（a-1）2a-a²/a²-a-2=（2-a）a/（a-2）（a+1）= -a/a+1原式=(a+1)/(a-1)-a/(a+1)=[(a+1)²-a(a-1)]/(a²-1)=(3a+1)/(a²-1)
