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E

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$\dfrac{3}{x}+\dfrac{9}{y} \ge 2.\dfrac{\sqrt{27}}{\sqrt{xy}}=6$

$3x+y \ge 2\sqrt{3xy}=6$

\Rightarrow $\dfrac{26}{3x+y} \le \dfrac{26}{6}=\dfrac{13}{3}$

\Rightarrow $P \ge 6-\dfrac{13}{3}=\dfrac{5}{3}$

Dấu = xảy ra \Leftrightarrow $xy=3;3x=y$
 
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