(x²-2x)(x²-2x+4)+3
=(x²-2x)[(x²-2x)+4]+3
=(x²-2x)²+4(x²-2x)+3
=[(x²-2x)+1][(x²-2x)+3]
=(x²-2x+1)(x²-2x+3)
=(x-1)²(x²-2x+3)