3xy-x-y=1 tìm x,y thuộc Z

Đáp án `+` Giải thích các bước giải:

 `3xy-x-y=1`

`<=>9xy-3x-3y=3`

`<=>3x(3y-1)-3y+1=3+1`

`<=>3x(3y-1)-(3y-1)=4`

`<=>(3y-1).(3x-1)=4=1.4=2.2-(-1).(-4)=(-2).(-2)`

Ta có bảng: 

\begin{array}{|c|c|c|}\hline \text{3x-1}&\text{1}&\text{4}&\text{-1}&\text{-4}&\text{2}&\text{-2}\\\hline \text{3y-1}&\text{4}&\text{1}&\text{-4}&\text{-1}&\text{2}&\text{-2}\\\hline \text{x}&\text{k t/m }&\text{k t/m}&\text{0}&\text{-1}&\text{1}&\text{k t/m}\\\hline \text{y}&\text{k t/m}&\text{k t/m}&\text{-1}&\text{0}&\text{k t/m}&\text{1}\\\hline\end{array}

   Vậy `(x;y)in{(0;-1);(-1;0)}`