原式=[(x-1)²/(x-3)²]×[-(x+3)(x-3)/(x-3)²]×1/(x-1)²
=-(x-1)²(x+3)(x-3)/[(x-3)²(x-3)²(x-1)²]
=-1/(x+3)(x-3)
=-1/(x²-9)