x³-3x²+4
=x³+x²-4x²+4
=x²(x+1)-4(x+1)(x-1)
=(x+1)(x²-4x+4)
=(x+1)(x-2)²
x³-7x+6
=x³-x²+x²-7x+6
=x²(x-1)+(x-1)(x-6)
=(x-1)(x²+x-6)
=(x-1)(x-2)(x+3)