`\color{#1c1c1c}{ccI}^(\color{#363636}{t}^(\color{#4f4f4f}{s}^(\color{#696969}{m}^(\color{#828282}{e}^(\color{#9c9c9c}{ccF}^(\color{#b5b5b5}{r}^(\color{#cfcfcf}{e}^\color{#eee9e9}{d})))))))`

Ta có:

`A = (3x - 7)/(x + 4)`

`A = (3x + 12 - 19)/(x + 4)`

`A = (3(x + 4) - 19)/(x + 4)`

   Vì `3(x + 4) vdots (x + 4)` nên để `A in NN` thì `19 vdots (x + 4)`

   `=> (x + 4) in Ư(19) = {+-1; +-19}`

   `=> x in {-3; -5; 15; -23}`

         Vậy: Để `A in NN` thì `x in {-3; -5; 15; -23}`