$VT \ge \frac{9}{\sqrt{a^2+bc}+\sqrt{b^2+ca}+\sqrt{c^2+ab}}$Vậy ta chỉ cần chứng minh $\sqrt{a^2+bc}+\sqrt{b^2+ca}+\sqrt{c^2+ab} \le \frac 32(a+b+c)$
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