1) \(xy-3x=-19\)
\(\Leftrightarrow x\left(3-y\right)=19=1\cdot19=\left(-1\right)\cdot\left(-19\right)\)
Ta có bảng sau:
| 3-y | 1 | 19 | -1 | -19 |
| x | 19 | 1 | -19 | -1 |
| y | 2 | -16 | 4 | 22 |
Vậy ...
2) \(3x+4y-xy=19\)
\(\Leftrightarrow xy-3x-4y=-19\)
\(\Leftrightarrow x\left(y-3\right)-4y=-19\)
\(\Leftrightarrow x\left(y-3\right)-\left(4y-12\right)=-7\)
\(\Leftrightarrow\left(x-4\right)\left(y-3\right)=-7=1\cdot\left(-7\right)=\left(-1\right)\cdot7\)
Ta có bảng sau:
| x-4 | 1 | 7 | -1 | -7 |
| y-3 | -7 | -1 | 7 | 1 |
| x | 5 | 11 | 3 | -3 |
| y | -4 | 2 | 10 | 4 |
Vậy...
