x平方-3x+2分之1 + x平方-5x+6分之1 + x平方-4x+3分之1
=1/(x-1)(x-2)+1/(x-2)(x-3)+1/(x-1)(x-3)
=(x-3+x-1+x-2)/[(x-1)(x-2)(x-3)
=(3x-6)/[(x-1)(x-2)(x-3)]
=3/[(x-1)(x-3)]