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