Tìm giá trị lớn nhất

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vipboycodon

$P = \dfrac{\sqrt{a-4}}{a}+\dfrac{\sqrt{b-9}}{b} = \dfrac{\sqrt{4(a-4)}}{2a}+\dfrac{\sqrt{9(b-9)}}{3b} \le \dfrac{4+a-4}{2.2a}+\dfrac{9+b-9}{2.3b} = \dfrac{5}{12}$
Dấu "=" xảy ra khi $a = 8$ , $b = 18$
 
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