x²-1/x²-4x+4 除以（x-1）乘以x-2/x²+x
=(x-1)(x+1)/(x-2)² ×1/(x-1)× (x-2)/x(x+1)
=(x-1)(x+1)(x-2)/[(x-2)²(x-1)x(x+1)]
=1/x(x-2)