4.Tìm các cặp số nguyên : $a) (a-2).b= -5 ; b) (a-1).(b+3)=7$ Y/c: càng nhanh càng tốt + đúng+ ko spam + ko coppy dưới mọi hình thức

`a, (a - 2).b = -5`

`=> -5 \vdots b`

`=> b \in Ư(-5)`

`=> b \in {+-1,+-5}`

Ta có bảng sau:

$$\begin{array}{|c|c|c|}\hline \text{b}&\text{1}&\text{-1}&\text{5}&\text{-5}\\\hline \text{a - 2}&\text{-5}&\text{5}&\text{-1}&\text{1}\\\hline \text{a}&\text{-3}&\text{7}&\text{1}&\text{3}\\\hline \text{Kết luận}&\text{thỏa mãn}&\text{thỏa mãn}&\text{thỏa mãn}&\text{thỏa mãn}\\\hline\end{array}$$

Vậy `(a,b) \in {(-3,1);(7,-1);(1,5);(3,-5)}`

`b, (a - 1)(b + 3) = 7`

`=> 7 \vdots a -1`

`=> a - 1 \in Ư(7)`

`=> a - 1 \in {+-1,+-7}`

Ta có bảng sau:

$$\begin{array}{|c|c|c|}\hline \text{a - 1}&\text{1}&\text{-1}&\text{7}&\text{-7}\\\hline \text{b + 3}&\text{7}&\text{-7}&\text{1}&\text{-1}\\\hline \text{a}&\text{2}&\text{0}&\text{8}&\text{-6}\\\hline \text{b}&\text{5}&\text{-10}&\text{-2}&\text{-4}\\\hline \text{Kết luận}&\text{thỏa mãn}&\text{thỏa mãn}&\text{thỏa mãn}&\text{thỏa mãn}\\\hline\end{array}$$

Vậy `(a,b) \in {(2,5);(0,-10);(8,-2);(-6,-4)}`