是a³/(a-1)-a²-a-1吧?= =+

已知：
a³-1
=(a-1)(a²+a+1)
则：
a³/(a-1)
=(a³-1)/(a-1)+1/(a-1)
=a²+a+1+1/(a-1)
代入原式,得：
a³/(a-1)-a²-a-1
=a²+a+1+1/(a-1)-a²-a-1
=1/(a-1)