x³-3x²+4
=x³+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