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Điều kiện $ x \ge 6 $
Ta có: $ \frac{{C_x^6{{\left( {2\frac{1}{3}} \right)}^{x - 6}}{{\left( {{3^{ - \frac{1}{3}}}} \right)}^6}}}{{C_x^{x - 6}{{\left( {{2^{\frac{1}{3}}}} \right)}^6}{{\left( {{3^{ - \frac{1}{3}}}} \right)}^{x - 6}}}} = \frac{1}{6}\,\,\, \Leftrightarrow \,\,\,\,\,\,{6^{ - 4}}{.6^{\frac{x}{3}}} = {6^{ - 1}}\,\,\, \Leftrightarrow \,\,\,x = 9 $
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