(x^2-x+1)/x=3x^2-x+1=3xx^2-4x+1=0同时除以xx-4+1/x=0所以x+1/x=4两边²x²+2+1/x²=16x²+1/x²=14所以：x^2/(x^4+x^2+1) 都除以x^2=1/(x^2+1+1/x^2)=1/(14+1)=1/15
