x2－4x+1=0
两边同除以x
x-4+(1/x)=0
x+(1/x)=4
(x+(1/x))^2=4^2=16
x^2+(1/x^2)=16-2=14
x2／[(x2)2－3x2+1]
=1/[x^2-3+(1/x^2)]
=1/[(x^2+(1/x^2))-3]
=1/(14-3)
=1/11