\(\frac{x}{5}=\frac{2}{x}\\ \Leftrightarrow x^2=10\\ \Leftrightarrow x^2=\left(\pm\sqrt{10}\right)^2\\ \Rightarrow x\in\left\{\sqrt{10};-\sqrt{10}\right\}\)
Vây ...
\(\frac{x}{5}=\frac{2}{x}\)
\(\Rightarrow x.x=2.5\)
\(\Rightarrow x.x=10\)
\(\Rightarrow x^2=10\)
\(\Rightarrow\left[{}\begin{matrix}x=\sqrt{10}\\x=-\sqrt{10}\end{matrix}\right.\)
Vậy \(x\in\left\{\sqrt{10};-\sqrt{10}\right\}.\)
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