Đáp án `+` Giải thích các bước giải`:`

`x−2y+xy=1`

`x+xy−2y−2=−1`

`x(1+y)−2(y+1)=−1` 

`(x−2)(y+1)=−1`

Suy ra `x−2;y+1∈Ư(−1)`

`Ư(−1)={−1;1}`

Ta có bảng sau`:`

\begin{array}{|c|c|c|}\hline \text{x-2}&\text{1}&\text{-1}\\\hline \text{y+1}&\text{-1}&\text{1}\\\hline \text{x}&\text{3}&\text{1}\\\hline \text{y}&\text{-2}&\text{0}\\\hline\end{array}

Suy ra `(x,y)∈{(1,0);(3,2)}`

Vậy `(x,y)∈{(1,0);(3,2)}`