[x-(x+1分之2x)]÷x²-1分之x²-2x+1
＝[x-(2x/x+1)]×[(x+1)(x-1)/(x-1)²]
＝[(x²-x)/(x+1)]×[(x+1)/(x-1)]
＝[x(x-1)/(x+1)]×[(x+1)/(x-1)]
＝x