a, \(\left(x-4\right)\left(2y-1\right)\inƯ\left(9\right)=\left\{\pm1;\pm3;\pm9\right\}\)
| x-4 | 1 | -1 | 3 | -3 | 9 | -9 |
| 2y-1 | -9 | 9 | -3 | 3 | -1 | 1 |
| x | 5 | 3 | 7 | 1 | 13 | -5 |
| y | -4 | 5 | -1 | 2 | 0 | 1 |
b, \(x\left(y-1\right)-3\left(y-1\right)=7\Leftrightarrow\left(x-3\right)\left(y-1\right)=7\)
\(\Rightarrow x-3;y-1\inƯ\left(7\right)=\left\{\pm1;\pm7\right\}\)
| x-3 | 1 | -1 | 7 | -7 |
| x | 4 | 2 | 10 | -4 |
c, \(xy-x-y=0\Leftrightarrow x\left(y-1\right)-\left(y-1\right)-1=0\Leftrightarrow\left(x-1\right)\left(y-1\right)=1\)
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