1/(x-2)(x-3)-1/(x-1)(x-3)+1/(x-1)(x-2)
=1/(x-3)-1/(x-2)-½[1/(x-3)-1/(x-1)]+1/(x-2)-1/(x-1)
=½×1/(x-3)-½×1/﹙x-1)
=½×2×1/(x-1)(x-3)
=1/(x-1)(x-3)
1/(x-2)(x-3)-1/(x-1)(x-3)+1/(x-1)(x-2)
=1/(x-3)-1/(x-2)-½[1/(x-3)-1/(x-1)]+1/(x-2)-1/(x-1)
=½×1/(x-3)-½×1/﹙x-1)
=½×2×1/(x-1)(x-3)
=1/(x-1)(x-3)