Tìm x,y biết xy+2y+x=6

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Ta có`:`

`xy+2y+x=6`

`xy+x+2y+2=6+2`

`x(y+1)+2(y+1)=8`

`(x+2)(y+1)=8`

Do `x,y in NN` nên `x+2;y+1 in Ư(8)`

`Ư(8)={+-1;+-2;+-4;+-8}`

Mà `x,y in NN` nên `x+2>=2`

Suy ra `x+2 in {2;4;8}`

Ta  có bảng sau`:`