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Dương Tuyết Lệ

\( 2^x + 2^{x+3} = 72 \)

\(2^x + 2^x \cdot 2^3 = 72\)

\(2^x + 8 \cdot 2^x = 72\)

\(9 \cdot 2^x = 72\)

\(2^x = 8\)

\(2^x = 2^3\)

\(x = 3\)

\( 9 : 27^x = \frac{1}{81} \)

\(\frac{9}{27^x} = \frac{1}{81}\)

\(9 = \frac{27^x}{81}\)

\(27^x = 9 \times 81\)

\(27^x = 729\)

\((3^3)^x = 3^6\)

\(3^{3x} = 3^6\)

\(3x = 6\)

\(x = 2\)

\( (5^x)^2 = 25^{11} \)

\(5^{2x} = (5^2)^{11}\)

\(5^{2x} = 5^{22}\)

\(2x = 22\)

\(x = 11\)