Resposta :

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[tex](3^x)^{x-4}= \frac{1}{27} \\ \\\not{3}^{x^2-4x}=\not{3}^{-3}\\ \\x^2-4x=-3\\x^2-4x+3=0\\ \\\Delta=(-4)^2-4.1.3\\\Delta=4\\ \\x= \frac{4\pm2}{2} \\ \\x_1=3\\ \\x_2=1[/tex]

[tex]\boxed{S=\{3 :1\}}[/tex]

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