X/(X^2-3X+1)=7可以写成(X^2-3X+1)/x=1/7 得x+1/x=22/7
X^2/(X^4+X^2+1)上下同除以X^2 得1/(x+1/x)^2-1
然后把x+1/x=22/7代进去就可以了