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Let $a,b,c≄0:ab+bc+ca=3$. Prove that:

$$\frac{\sqrt{a+3}}{a+\sqrt{bc}}+\frac{\sqrt{b+3}}{b+\sqrt{ca}}+\frac{\sqrt{c+3}}{c+\sqrt{ab}}\ge\frac{2(\sqrt{a}+\sqrt{b}+\sqrt{c})}{\sqrt{a+b+c+1}}$$ This is really tough problem. I tried to use AM-GM as: $$2\sqrt{a+3}=2\sqrt{\frac{a+ab+bc+ca}{a+\sqrt{bc}}(a+\sqrt{bc})}\le\frac{a(a+b+c+1)}{a+\sqrt{bc}}+2\sqrt{bc}$$ But it seems useless. "sqrt" is a big ostacle. Is there any better idea? Thanks for all.

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