Giải thích các bước giải:
\(\begin{array}{l}
a.n \in U\left( {10} \right)\\
\to \left[ \begin{array}{l}
n = 10\\
n = - 10\\
n = 5\\
n = - 5\\
n = 2\\
n = - 2\\
n = 1\\
n = - 1
\end{array} \right.\\
b.\left( {n + 2} \right) \in U\left( {20} \right)\\
\to \left[ \begin{array}{l}
n + 2 = 20\\
n + 2 = - 20\\
n + 2 = 10\\
n + 2 = - 10\\
n + 2 = 5\\
n + 2 = - 5\\
n + 2 = 4\\
n + 2 = - 4\\
n + 2 = 2\\
n + 2 = - 2\\
n + 2 = 1\\
n + 2 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
n = 18\\
n = - 22\\
n = 8\\
n = - 12\\
n = 3\\
n = - 7\\
n = 2\\
n = - 6\\
n = 0\\
n = - 4\\
n = - 1\\
n = - 3
\end{array} \right.\\
c.n - 1 \in U\left( {12} \right)\\
\to \left[ \begin{array}{l}
n - 1 = 12\\
n - 1 = - 12\\
n - 1 = 6\\
n - 1 = - 6\\
n - 1 = 4\\
n - 1 = - 4\\
n - 1 = 3\\
n - 1 = - 3\\
n - 1 = 2\\
n - 1 = - 2\\
n - 1 = 1\\
n - 1 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
n = 13\\
n = - 11\\
n = 7\\
n = - 5\\
n = 5\\
n = - 3\\
n = 4\\
n = - 2\\
n = 3\\
n = - 1\\
n = 2\\
n = 0
\end{array} \right.\\
d.2n + 3 \in U\left( {10} \right)\\
\to \left[ \begin{array}{l}
2n + 3 = 10\\
2n + 3 = - 10\\
2n + 3 = 5\\
2n + 3 = - 5\\
2n + 3 = 2\\
2n + 3 = - 2\\
2n + 3 = 1\\
2n + 3 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
n = \frac{7}{2}\left( l \right)\\
n = \frac{{ - 13}}{2}\left( l \right)\\
n = 1\\
n = - 4\\
n = - \frac{1}{2}\left( l \right)\\
n = - \frac{5}{2}\left( l \right)\\
n = - 1\\
n = - 2
\end{array} \right.
\end{array}\)
