Giải thích các bước giải:
\(\begin{array}{l}
a.\left( {2n + 3} \right) \in U\left( 5 \right)\\
\to \left[ \begin{array}{l}
2n + 3 = 5\\
2n + 3 = - 5\\
2n + 3 = 1\\
2n + 3 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
n = 1\\
n = - 4\\
n = - 1\\
n = - 2
\end{array} \right.\\
b.\left( {n - 3} \right) \vdots \left( {n + 4} \right)\\
\to n + 4 - 7 \vdots \left( {n + 4} \right)\\
\to \left( {n + 4} \right) \in U\left( 7 \right)\\
\to \left[ \begin{array}{l}
n + 4 = 7\\
n + 4 = - 7\\
n + 4 = 1\\
n + 4 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
n = 3\\
n = - 11\\
n = - 3\\
n = - 5
\end{array} \right.
\end{array}\)
