x^4-x^3 -6x^3+6x^2+11x^2-11x-6x+6=x^3(x-1)-6x^2(x-1) +11x(x-1)-6(x-1)=(x-1)(x^3-6x^2+11x-6)=(x-1) [x^2(x-1)-5x(x-1)+6(x-1)]=(x-1)^2(x^2-5x+6)=(x-1)^2(x-2)(x-3)