a方+2a+1分之a方-1-a方分之a方+2a=a²/(a+1)²+a(a+1)/(a²-1)=a²/(a+1)²+a(a+1)/(a+1)(a-1)=a²(a+1)²+a/(a-1)=[a²(a-1)+a]/(a+1)²(a-1)=(a³-a²+a)/(a+1)²...