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Cho điều kiện : a,b,c > 0. CM
$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}>=3(\frac{1}{a+2b}+\frac{1}{b+2c}+\frac{1}{c+2a})$
$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}>=3(\frac{1}{a+2b}+\frac{1}{b+2c}+\frac{1}{c+2a})$