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\(\sqrt{x+6}-2\sqrt{x}>0\)
\(\Leftrightarrow\sqrt{x+6}>2\sqrt{x}\)
\(\Leftrightarrow x+6>4x\)
\(\Leftrightarrow-3x>-6\)
\(\Leftrightarrow x
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\(x\ge m\)
\(\sqrt{x-m+2\sqrt{m\left(x-m\right)}+m}+\sqrt{x-m-2\sqrt{m\left(x-m\right)}+m}\le2\)
\(\Leftrightarrow\sqrt{\left(\sqrt{x-m}+\sqrt{m}\right)^2}+\sqrt{\left(\sqrt{x-m}-\sqrt{m}\right)^2}\le2\)
\(\Leftrightarrow\sqrt{x-m}+\sqrt{m}+\left|\sqrt{x-m}-\sqrt{m}\right|\le2\)
- Nếu \(\sqrt{x-m}\ge\sqrt{m}\Leftrightarrow x\ge2m\) BPT trở thành:
\(2\sqrt{x-m}\le2\Leftrightarrow x\le m+1\Rightarrow2m\le x\le m+1\)
\(\Rightarrow m+1\ge2m\Rightarrow m\le1\)
- Nếu \(\sqrt{x-m}< \sqrt{m}\Leftrightarrow m\le x< 2m\) BPT trở thành:
\(2\sqrt{m}\le2\Rightarrow m\le1\)
Vậy nếu \(0< m\le1\) thì BPT có nghiệm \(m\le x\le m+1\)
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ĐKXĐ: \(-1\le x\le7\)
Ta có: \(VT\le\sqrt{2\left(x+1+7-x\right)}=4\)
\(VP=\left(x-3\right)^2+4\ge4\)
\(\Rightarrow VT\le VP\)
\(\Rightarrow\) BPT có nghiệm khi \(VT=VP\Leftrightarrow\left\{{}\begin{matrix}x+1=7-x\\x-3=0\end{matrix}\right.\) \(\Rightarrow x=3\)
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bài 2
ta có \(\left(\sqrt{8a^2+1}+\sqrt{8b^2+1}+\sqrt{8c^2+1}\right)^2\)
\(=\left(\sqrt{a}.\sqrt{\frac{8a^2+1}{a}}+\sqrt{b}.\sqrt{\frac{8b^2+1}{b}}+\sqrt{c}.\sqrt{\frac{8c^2+1}{c}}\right)^2\)\(=\left(A\right)\)
Áp dụng bất đẳng thức Bunhiacopxki ta có;
\(\left(A\right)\le\left(a+b+c\right)\left(8a+\frac{1}{a}+8b+\frac{1}{b}+8c+\frac{8}{c}\right)\)
\(=\left(a+b+c\right)\left(9a+9b+9c\right)=9\left(a+b+c\right)^2\)
\(\Rightarrow3\left(a+b+c\right)\ge\sqrt{8a^2+1}+\sqrt{8b^2+1}+\sqrt{8c^2+1}\)(đpcm)
Dấu \(=\)xảy ra khi \(a=b=c=1\)
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\(x\left(x-1\right)>0\)
\(\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>0\\x-1>0\end{matrix}\right.\\\left\{{}\begin{matrix}x< 0\\x-1< 0\end{matrix}\right.\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x>1\\x< 0\end{matrix}\right.\)