设3x^2-kx-5k+1=(x+1)(3x+m)＝3x^2+3x+mx+m=3x^2+(3+m)x+m,则3+m=-k-5k+1=m从而，3-5k+1=-k,k=1
3x^2-x-4=(x+1)(3x-4)当x+1=0时 x= -1 3x^2-kx-5k+1=0 k=1
