${{\log }_{3}}\left( {{\left( {{\log }_{2}}x \right)}^{2}}+3{{\log }_{2}}x+5 \right)=2\,\,\left( 1 \right)$

Đk: $\left\{ \begin{align}  & x>0 \\  & {{\left( {{\log }_{2}}x \right)}^{2}}+3{{\log }_{2}}x+5>0 \\ \end{align} \right.$

$\left( 1 \right)\Leftrightarrow {{\left( {{\log }_{2}}x \right)}^{2}}+3{{\log }_{2}}x+5=9\Leftrightarrow {{\left( {{\log }_{2}}x \right)}^{2}}+3{{\log }_{2}}x-4=0\Leftrightarrow x=2$ hoặc $x=\frac{1}{16}$