1. Cho $x,y,z \in \mathbb R.$ Chứng minh:
$\sqrt{x^{2}+xy+y^{2}} + \sqrt{y^{2}+yz+z^{2}} \geq \sqrt{x^{2}+xz+z^{2}}$2. Cho $a,b,c>0 , ab+bc+ca=abc$.CMR $\color{red} {\frac{\sqrt{b^2+2a^2}}{ab}+\frac{\sqrt{c^2+2b^2}}{bc}+\frac{\sqrt{a^2+2c^2}}{ca}\geq 3}$