Phương trình ${{9}^{x}}-{{3.3}^{x}}+2=0$ có hai nghiệm...

Ta có: $\left[ \begin{aligned}
& {{3}^{x}}=1 \\
& {{3}^{x}}=2 \\
\end{aligned} \right.$$\Leftrightarrow \left[ \begin{aligned}
& x=0 \\
& x={{\log }_{3}}2 \\
\end{aligned} \right.{{x}_{1}}<{{x}_{2}}{{x}_{1}}=0,{{x}_{2}}={{\log }_{3}}22{{x}_{1}}+3{{x}_{2}}=2.0+3.{{\log }_{3}}2=3{{\log }_{3}}2$.