de= (3x^2-3xy+3y^2)/3(x^2+xy+y^2)=((x^2+xy+y^2)+2(x-y)^2)/3(x^2+xy+y^2)=1/3+((x-y)^2)/(x^2+xy+y^2)\geq1/3de=(3(x^2+xy+y^2)-2(x+y)^2)/(x^2+y^2+xy)=3+2(x+y)^2)/(x^2+y^2+xy)\leq3
de
$= (3x^2-3xy+3y^2)/3(x^2+xy+y^2)=((x^2+xy+y^2)+2(x-y)^2)/3(x^2+xy+y^2)=1/3+((x-y)^2)/(x^2+xy+y^2)\geq1/3
$de
$=(3(x^2+xy+y^2)-2(x+y)^2)/(x^2+y^2+xy)=3+2(x+y)^2)/(x^2+y^2+xy)\leq3
$