x2-5x+6/x2-4x+3 + x2-4x+3/x2-2x+1 + x2-3x-4/1-x2 =(x-2)(x-3)/(x-3)(x-1)+(x-3)(x-1)/(x-1)²-(x-4)(x+1)/(x+1)(x-1)=(x-2)/(x-1)+(x-3)/(x-1)-(x-4)/(x-1)=(x-2+x-3-x+4)/(x-1)=(x-1)/(x-1)=1