x^2/(x^4+x^2+1) 取倒数好拿(x^4+x^2+1)/x^2=x^2+1+1/x^2=x^2+2+1/x^2-1=(x+1/x)^2-1=3^2-1=8 (取倒数)所以友灶搭辩纳x^2/(x^4+x^2+1)=1/8
1\8
