$\begin{array}{l}\text{- Ta có :}\ \overline{abcdeg}=\overline{abc000}+\overline{deg}\\\to\overline{abcdeg}=1000.\overline{abc}+\overline{deg}\\\to \overline{abcdeg}=1000.\left(2.\overline{deg}\right)+\overline{deg}\\\to \overline{abcdeg}=2000.\overline{deg}+\overline{deg}\\\to \overline{abcdeg}=2001.\overline{deg}\\\to\overline{abcdeg}=87.23.\overline{deg}\\\to\overline{abcdeg}\ \vdots\ 87\\\text{- Vậy $\overline{abcdeg}\ \vdots\ 87\ \forall\ \overline{abc}=2.\overline{deg}$} \end{array}$
