x^2-4x+1=0
易证x≠0
等式两边除以x得
x-4+1/x=0
x+1/x=4
(x+1/x)^2=16
x^2+2+1/x^2=16
x^2-2+1/x^2=12
(x-1/x)^2=12
x-1/x=±2√3