1/27-x+9x²-27x³
=1/27-x+6x²+3x²-27x³
=﹙3x-1／3﹚﹙2x－1／9﹚－9x²﹙3x-1／3﹚
=﹙3x-1／3﹚﹙2x－1／9－9x²﹚
=﹙3x-1／3﹚[﹣﹙3x-1／3﹚²]
=﹣﹙3x-1／3﹚³
6x²-7xy-20y²=﹙3x＋4y﹚﹙2x-5y﹚