a) Ta có: \(xy=-13\)
\(\Leftrightarrow x,y\inƯ\left(-13\right)\)
\(\Leftrightarrow x,y\in\left\{1;-1;13;-13\right\}\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}x=1\\y=-13\end{matrix}\right.\\\left\{{}\begin{matrix}x=-1\\y=13\end{matrix}\right.\\\left\{{}\begin{matrix}x=-13\\y=1\end{matrix}\right.\\\left\{{}\begin{matrix}x=13\\y=-1\end{matrix}\right.\end{matrix}\right.\)
Vậy: (x,y)∈{(1;-13);(-1;13);(-13;1);(13;-1)}
b) Ta có: \(\left(x-1\right)\left(y+2\right)=7\)
\(\Leftrightarrow x-1;y+2\inƯ\left(7\right)\)
\(\Leftrightarrow x-1;y+2\in\left\{1;7;-1;-7\right\}\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}x-1=1\\y+2=7\end{matrix}\right.\\\left\{{}\begin{matrix}x-1=7\\y+2=1\end{matrix}\right.\\\left\{{}\begin{matrix}x-1=-1\\y+2=-7\end{matrix}\right.\\\left\{{}\begin{matrix}x-1=-7\\y+2=-1\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}x=2\\y=5\end{matrix}\right.\\\left\{{}\begin{matrix}x=8\\y=-1\end{matrix}\right.\\\left\{{}\begin{matrix}x=0\\y=-9\end{matrix}\right.\\\left\{{}\begin{matrix}x=-6\\y=-3\end{matrix}\right.\end{matrix}\right.\)
Vậy: (x,y)∈{(2;5);(8;-1);(0;-9);(-6;-3)}
