(x+y)(x-2y+1)=5 giải ptr nghiệm nguyên . (x;y Z)

`(x+ y)(x - 2y + 1) = 5`

Ta có bảng sau:

\begin{array}{|c|c|c|}\hline \text{x + y}&\text{1}&\text{-1}&\text{5}&\text-5{}\\\hline \text{x - 2y + 1}&\text{5}&\text{-5}&\text{1}&\text{-1}\\\hline \text{x - 2y}&\text{4}&\text{-6}&\text{0}&\text{-2}\\\hline \text{x}&\text{2}&\text{$\frac{-8}{3}$}&\text{$\frac{10}{3}$}&\text{-4}\\\hline \text{y}&\text{-1}&\text{$\frac{5}{3}$}&\text{$\frac{5}{3}$}&\text{-1}\\\hline \text{Kết luận}&\text{thỏa mãn}&\text{loại}&\text{loại}&\text{thỏa mãn}\\\hline\end{array}

Vậy `(x,y) \in {(2,-1);(-4,-1)}`