由x²-2x-1=0,得x²-2x=1,（x-1）²=2
x^4-x³-5x²-7x+5=x^4-x³-5（x²-2x）-17x+5
=x^4-x³-17x=x²（x²-2x）+x³-17x=x³+x²-17x
=x（x²-2x）+3x²-17x=3x²-16x
=3（x²-2x）-10x=3-10x= -10（x-1）-7
=-10根号2-7
或=10根号2-7