Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
1,\\
a,\\
{2^{x + 2}} + {2^x} = 5.16\\
\Leftrightarrow {2^x}{.2^2} + {2^x} = 5.16\\
\Leftrightarrow {2^x}.\left( {{2^2} + 1} \right) = 5.16\\
\Leftrightarrow {2^x}.5 = 5.16\\
\Leftrightarrow {2^x} = 16\\
\Leftrightarrow x = 4\\
b,\\
x + 15 = \left( {x + 2} \right) + 13\\
\left( {x + 15} \right)\,\, \vdots \,\,\,\left( {x + 2} \right)\\
\Rightarrow \left[ {\left( {x + 2} \right) + 13} \right]\,\, \vdots \,\,\left( {x + 2} \right)\\
\Rightarrow 13\,\, \vdots \,\,\left( {x + 2} \right)\\
\Rightarrow \left[ \begin{array}{l}
x + 2 = 1\\
x + 2 = 13
\end{array} \right. \Rightarrow x = 11\\
2,\\
A\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{7^{17}} + 17.3 - 1} \right)\,\, \vdots \,\,9\\
\Leftrightarrow 7.\left( {{7^{17}} + 17.3 - 1} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{{7.7}^{17}} + 7.17.3 - 7} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{7^{18}} + 119.3 - 7} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{7^{18}} + 117.3 + 2.3 - 7} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{7^{18}} + 117.3 + 6 - 7} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left( {{7^{18}} + 117.3 - 1} \right)\,\, \vdots \,\,9\\
\Leftrightarrow \left[ {\left( {{7^{18}} + 18.3 - 1} \right) + 99.3} \right]\,\, \vdots \,\,9\\
99\,\, \vdots \,\,9 \Rightarrow \left( {{7^{18}} + 18.3 - 1} \right)\,\, \vdots \,\,9 \Rightarrow B\,\, \vdots \,\,9
\end{array}\)
