[Đại 9]: Cực trị!!!

E

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$\dfrac{\sqrt{x-1}-2\sqrt{2-x}+3}{\sqrt{x-1}+2\sqrt{2-x}+3}=1-\dfrac{4\sqrt{2-x}}{\sqrt{x-1}+2\sqrt{2-x}+3}$ \leq $1$
Dấu "=" xảy ra \Leftrightarrow $x=2$
 
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