$\Rightarrow P=\frac{1}{2+3a}+\frac{1}{1+b}+\frac{1}{1+c}\geq \frac{1}{2+3a}+\frac{2}{1+\sqrt{bc}}=\frac{1}{2+3a}+\frac{2\sqrt{a}}{\sqrt{a}+1}$
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$\frac{1}{1+b} + \frac{1}{1+c} \geq \frac{2}{1+\sqrt{bc}}$ . Bạn giải thích chỗ nãy rõ dk ko