x^2=2x+1
x^3=2x^2+x=2(2x+1)+x=5x+2
x^4=x(5x+2)=5(2x+1)+2x=12x+5
x^4-x^3-5x^2-7x+5
=12x+5-(5x+2)-5(2x+1)-7x+5
=3-10x
x^2-2x+1=2
x=1±√2
所以原式=3-10x=3-10(1±√2)=-7±10√2