解﹕﹙x²-1﹚﹙x⁴+x²+1﹚-﹙x³+1﹚²
=﹙x⁶-1﹚-﹙x³+1﹚²
=﹙x³+1﹚﹙x³-1﹚-﹙x³+1﹚²
=﹙x³+1﹚﹙x³-1-x³-1﹚
=-2（x+1）（x²-x+1）．