x=3分之4-√7,所以4-3x=√7,两边平方后化简得到3x^2-8x+3=0,
x+1/x=8/3
x^2/(x^4+x^2+1)=1/(x^2+1+1/x^2)=1/[(x+1/x)^2-1]=9/55