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Theo giả thiết:
$ \begin{array}{l}
C_6^3{x^{\frac{3}{{2\left( {\lg x + 1} \right)}}}}{x^{\frac{1}{4}}} = 200\,\,\,\, \Leftrightarrow \,\,\,\,\,20{x^{\frac{1}{4} + \frac{3}{{2\left( {\lg x + 1} \right)}}}} = 200\\
\Leftrightarrow \left( {\frac{1}{4} + \frac{3}{{2\left( {\lg x + 1} \right)}}} \right)\lg x = 1\,\, \Leftrightarrow \lg x = - 4 \vee \lg x = 1\\
\Leftrightarrow \,\,\,x = \frac{1}{{{{10}^4}}} \vee x = 10
\end{array} $
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