|
|
Ta có: $ C_5^2{x^3}{x^{2\lg x}} = 10.{x^{3 + 2\lg x}} = {10^6} \Leftrightarrow {x^{3 + 2\lg x}} = 10^5 $
$ \begin{array}{l}
\Leftrightarrow \,\,\,\,\,\,\left[ {3 + 2\lg x} \right]\lg x = 5\,\,\, \Leftrightarrow \,\,\,\,2{\left( {\lg x} \right)^2} + 3\lg x - 5 = 0\\
\Leftrightarrow \,\,\,\,\,\lg x = 1 \vee \lg = - \frac{5}{2}\,\,\,\,\,\, \Leftrightarrow \,\,\,x = 10 \vee x = {10^{\frac{{ - 5}}{2}}}\,\,\, &
\end{array} $
|