kx²+k²x+2kx+2x-k²-k+6
=(k²x-k²)+(kx²+2kx-k)+2x+6
=(x-1)k²+(x²+2x-1)k+2(x+3)
=[(x-1)k+2][k+(x+3)]
=(kx-k+2)(x+k+3)