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