Question

${3}^{x} - {3}^{x - 2} = 72$
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Answer 1

Ответ:

${3}^{x} - {3}^{ x - 2} = 72$

${3}^{x} - {3}^{x} \times {3}^{ - 2} =72$

${3}^{x} (1 - {3}^{ - 2} ) = 72$

${3}^{x} (1 - \frac{1}{9} ) = 72$

$\frac{8}{9} \times {3}^{x} = 72$

${3}^{x} = 72 \times \frac{9}{8}$

${3}^{x} = 81$

${3}^{x} = {3}^{4}$

$x = 4$

Answer 2

Ответ:   x=4 .

Объяснение:

$3^{x}-3^{x-2}=72\\\\3^{x}-\frac{3^{x}}{3^2}=72\\\\3^{x}\cdot (1-\frac{1}{9})=72\\\\3^{x}\cdot \frac{8}{9}=72\\\\3^{x}=\frac{72\cdot 9}{8}\\\\3^{x}=81\\\\3^{x}=3^4\\\\\underline {x=4}$