Question:
let $x,y,z\ge 0$.prove or disprove
$$\dfrac{3(x^2+y^2+z^2)}{(x+y+z)^2+2(yz+xz+xy)}\ge\sum\limits_{cyc}\dfrac{x^2}{x^2+(y+z)^2}$$
My idea: let $x+y+z=1$, then we can only $$\sum_{cyc}\dfrac{x^2}{x^2+(y+z)^2}=\sum_{cyc}\dfrac{x^2}{2x^2-2x+1}\le\dfrac{3(x^2+y^2+z^2)}{1+2(xy+yz+xz)}$$
then I can't.Thank you
It's wrong! Try $x=4$ and $y=z=9$.