Giải thích các bước giải:
\(\begin{array}{l}
5,\\
\overline {abc\deg } = \overline {ab0000} + \overline {cd00} + \overline {eg} \\
= 10000.\overline {ab} + 100\overline {cd} + \overline {eg} \\
= \left( {9999\overline {ab} + 99\overline {cd} } \right) + \left( {\overline {ab} + \overline {cd} + \overline {eg} } \right)\\
= \left( {11.909.\overline {ab} + 11.9\overline {.cd} } \right) + \left( {\overline {ab} + \overline {cd} + \overline {eg} } \right)\\
= 11.\left( {909.\overline {ab} + 9.\overline {cd} } \right) + \left( {\overline {ab} + \overline {cd} + \overline {eg} } \right)\\
11.\left( {909.\overline {ab} + 9.\overline {cd} } \right)\,\, \vdots \,\,11\\
\left( {\overline {ab} + \overline {cd} + \overline {eg} } \right)\,\, \vdots \,\,11\\
\Rightarrow \left[ {11.\left( {909.\overline {ab} + 9.\overline {cd} } \right) + \left( {\overline {ab} + \overline {cd} + \overline {eg} } \right)} \right]\,\, \vdots \,\,11\\
\Rightarrow \overline {abc\deg } \,\, \vdots \,\,11\\
6,\\
{3^7}.25 - {3^9}\\
= {3^7}.25 - {3^{7 + 2}}\\
= {3^7}.25 - {3^7}{.3^2}\\
= {3^7}.\left( {25 - {3^2}} \right)\\
= {3^7}.16\,\, \vdots \,\,8
\end{array}\)
