Ta có: \(xy+12=x+y\)
\(\Leftrightarrow xy-x-y=12\)
\(\Leftrightarrow x\left(y-1\right)-\left(y-1\right)=13\)
\(\Leftrightarrow\left(x-1\right)\left(y-1\right)=13=1.13=13.1=-1.-13=-13.-1\)
\(\Leftrightarrow\left[{}\begin{matrix}x-1=1;y-1=13\\x-1=13;y-1=1\\x-1=-1;y-1=-13\\x-1=-13;y-1=-1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2;y=14\\x=14;y=2\\x=0;y=-12\\x=-12;y=0\end{matrix}\right.\)
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