·已知x^2－3x+1=0，求二次根号下（x^2+1/x^2－2?
x²-3x+1=0 x-3+1/x=0 x+1/x=3 x²+1/x²=(x+1/x)²-2=7 ===>√(x²+1/x²－2) =√5