Đáp án:
\(x \in \left\{ {0;\,\,4;\,\,18} \right\}.\)
Giải thích các bước giải:
\(\begin{array}{l}
x \in N \Rightarrow x + 3 \ge 3.\\
x + 24\,\,la\,\,boi\,\,\,cua\,\,x + 3\\
\Rightarrow x + 24\,\,\,chia\,\,\,het\,\,cho\,\,\,x + 3\\
Ma\,\,\,x + 3\,\,\,\,chia\,\,het\,\,cho\,\,\,x + 3\\
\Rightarrow \left( {x + 24 - x - 3} \right)\,\,\,\,chia\,\,het\,\,\,cho\,\,\,x + 3\\
\Rightarrow 21\,\,\,chia\,\,\,het\,\,\,cho\,\,\,x + 3\\
Ma\,\,\,21\,\,\,chia\,\,het\,\,cho\,\,1;\,\,3;\,\,7;\,\,21\\
Vi\,\,\,x + 3 \ge 3\\
\Rightarrow \left[ \begin{array}{l}
x + 3 = 3\\
x + 3 = 7\\
x + 3 = 21
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x = 4\\
x = 18
\end{array} \right..\\
Vay\,\,\,x \in \left\{ {0;\,\,4;\,\,18} \right\}.
\end{array}\)
