Đáp án:
$\begin{array}{l}
480 = {2^5}.3.5\\
240 = {2^4}.3.5\\
720 = {2^4}{.3^2}.5\\
\Rightarrow BCNN\left( {480;240;720} \right) = {2^5}{.3^2}.5 = 1440\\
{\left( {3x - 8} \right)^{10}} = {\left( {3x - 8} \right)^{12}}\\
\Rightarrow {\left( {3x - 8} \right)^{10}}.\left( {1 - {{\left( {3x - 8} \right)}^2}} \right) = 0\\
\Rightarrow \left[ \begin{array}{l}
3x - 8 = 0\\
1 - {\left( {3x - 8} \right)^2} = 0
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = \frac{8}{3}\\
3x - 8 = 1\\
3x - 8 = - 1
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = \frac{8}{3}\\
x = 3\\
x = \frac{7}{3}
\end{array} \right.
\end{array}$
