\(a;\sqrt{x-3}+\sqrt{15-x}\le\sqrt{2\left(x-3+15-x\right)}=2\sqrt{6}\)\(\left(đk:3\le x\le15\right)\)
\(dấu"="\) \(xảy\) \(ra\Leftrightarrow\sqrt{x-3}=\sqrt{15-x}\Leftrightarrow x-3=15-x\Leftrightarrow x=9\left(tm\right)\)
\(b;\sqrt{\dfrac{x}{2x-1}}+\sqrt{\dfrac{2x-1}{x}}\ge2\sqrt{\sqrt{\dfrac{x}{2x-1}}.\sqrt{\dfrac{2x-1}{x}}}=2\)
\(dấu"="\Leftrightarrow\sqrt{\dfrac{x}{2x-1}}=\sqrt{\dfrac{2x-1}{x}}\Leftrightarrow x=1\) thhuer vào thấy thỏa mãn
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