xy = 30
=> \(x,y\in\)Ư(30)
=> \(x,y\in\left\{1;2;3;5;6;10;15;30\right\}\)
x ( y + 2 ) = 15
=> x, y+ 2 \(\inƯ\left(15\right)\)
= \(x,y+2\in\left\{1;3;5;15\right\}\)
\(xy=30\)
\(\Rightarrow\left(x,y\right)=\left(1,30\right);\left(30,1\right);\left(5,6\right);\left(6,5\right);\left(15,2\right);\left(2,15\right);\left(3,10\right);\left(10,3\right)\)
\(x\left(y+2\right)=15\)
\(\Rightarrow\)Ta có bảng sau :
| y+2 | 3 | 5 | 1 | 15 |
| y | 1 | 3 | y\(\notin\)N | 13 |
| x | 5 | 3 | 15 | 1 |
xy + 7y + x = 19
\(\Rightarrow\)y(x+7) + x + 7 = 26
\(\Rightarrow\)( x + 7 ) ( y + 1) = 26
\(\Rightarrow\)ta có bảng sau :
| x+7 | 1 | 26 | 2 | 13 |
| y+1 | 26 | 1 | 13 | 2 |
| x | \(x\notin N\) | 19 | \(x\notin N\) | 6 |
| y | 25 | \(y\notin N\) | 12 | \(y\notin N\) |
\(xy=30\Rightarrow x;y\inƯ\left(30\right)\)
\(x\left(y+2\right)=15\Rightarrow xy+2x=15\)\(\Rightarrow3x+y=15\)\(\Rightarrow3x+y\inƯ\left(15\right)\)
\(xy+7y+x=19\Rightarrow3x+8y=19\Rightarrow3x+8y\inƯ\left(19\right)\)
