2/1是二分之一嘛?如果是的话.(2/1+a)-(a-2/a-1)÷(a²-2a/a²-2a+1)=（2/1+a-a+2/a+1）÷（a²-2/a-2a+1）=[2/（1+a+2）×2]÷[(a²-2a+1）-2/a×2]=（1+a+2）÷[2(a-1）²-a]=（a+3）÷[2(a-1...