x³－3x²＋x＋1
=x³－2x²＋x－x²＋1
=x(x-1)²-(x-1)(x+1)
=(x-1)[x(x-1)-(x+1)]
=(x-1)(x²-2x-1)
当x－1>0,即x>1时,
x²-2x-1