Đáp án:
$\begin{array}{l}
3)\\
a)19 \vdots \left( {x - 2} \right) \Rightarrow \left[ \begin{array}{l}
x - 2 = 1\\
x - 2 = 19
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = 3\\
x = 21
\end{array} \right.\\
4)\\
a)\left( {x - 2} \right).\left( {y + 1} \right) = 17\\
\Rightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x - 2 = 17\\
y + 1 = 1
\end{array} \right.\\
\left\{ \begin{array}{l}
x - 2 = 1\\
y + 1 = 17
\end{array} \right.
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x = 19\\
y = 0
\end{array} \right.\\
\left\{ \begin{array}{l}
x = 3\\
y = 16
\end{array} \right.
\end{array} \right.\\
Vậy\,\left( {x;y} \right) = \left( {19;0} \right)hoac\,\left( {3;16} \right)
\end{array}$
