Tìm a,b ∈ Z biết : ab + a = -15

Đáp án:

`↓`

Giải thích các bước giải:

`ab + a = -15`

`=> a * b + a * 1 = -15`

`=> a * ( b + 1 ) = -15`

`=> a; b + 1 \in Ư(-15) = { -15; -5; -3; -1; 1; 3; 5; 15 }`

Ta có bảng:

$\begin{array}{|c|c|c|}\hline \text{a}&\text{-15}&\text{-5}&\text{-3}&\text{-1}&\text{1}&\text{3}&\text{5}&\text{15}\\\hline \text{b + 1}&\text{1}&\text{3}&\text{5}&\text{15}&\text{-15}&\text{-5}&\text{-3}&\text{-1}\\\hline \text{b}&\text{0}&\text{2}&\text{4}&\text{14}&\text{-16}&\text{-6}&\text{-4}&\text{-2}\\\hline\end{array}$

Vậy ...

`#Sad`