（1/2x+2)-（x/x^2-1）+（1/x-1）
=1/2(x+1)- x/(x+1)(x-1）+1/(x-1）
=1/2(x+1)- x/(x+1)(x-1）+1/(x-1）
=(x-1-2x+2x+2)/2(x+1)(x-1)
=(x+1)/2(x+1)(x-1)
=1/2(x-1)
=1/(2x-2)