x³-kx²-x+3=(x-1)(ax²+bx+c)=ax³+(b-a)x²+(c-b)x-ca=1 -c=3 c=-3 c-b=-1 b=c+1=-2 b-a=k=-2-1=-3所以 k=-3 x³+-3x²-x+3=(x-1)(x²-2x-3)=(x-1)(x-3)(x+1)