81log x + 9log x + 3log x = 7 cara nya gimana kalo soalnya kaya begini???

[tex]^{81}\log{x}+^{9}\log{x}+^{3}\log{x}=7 \\ ^{3^4}\log{x}+^{3^2}\log{x}+^{3}\log{x}=7 \\ \frac{1}{4}^3\log{x}+\frac{1}{2}^3\log{x}+^3\log{x}=7 \\ \frac{7}{4}^3\log{x}=7 \\ ^3\log{x}=7\times \frac{4}{7} \\ ^3\log{x}=4 \\ x=3^4=81[/tex]