Ta có: ` ( x-1 ) . ( 2y + 1 ) = 26`
`=>{(x-1 \in Ư(26)),(2y + 1\in Ư(26) ):}`
Ta có:
`Ư(26)={1;2;13;26}`
`=>` Ta có bảng sau:
\begin{array}{|c|c|c|}\hline \text{x-1}&\text{1}&\text{2}&\text{13}&\text{26}\\\hline \text{2y+1}&\text{26}&\text{13}&\text{2}&\text{1}\\\hline \text{x}&\text{3}&\text{2}&\text{14}&\text{27}\\\hline \text{y}&\text{6}&\text{12,5}&\text{6,5}&\text{0}\\\hline\end{array}
Mà `x;y \inNN`
`=>` Các cặp số `(x;y)` thoả mãn là:
`(3;6);(27;0)`
