$\\$
`3x+4 \vdots x+3`
`->3x + 9 - 5 \vdots x+3`
`-> 3 (x+3)-5 \vdots x+3`
Vì `x+3 \vdots x+3 ->3 (x+3) \vdots x+3`
`-> 5 \vdots x+3`
`->x+3 ∈ Ư (5)={1;-1;5;-5}`
$\bullet$ `x+3=1 ->x=-2` (Thỏa mãn)
$\bullet$ `x+3=-1 ->x=-4` (Thỏa mãn)
$\bullet$ `x+3=5 ->x=2` (Thỏa mãn)
$\bullet$ `x+3=-5 ->x=-8`(Thỏa mãn)
Vậy `x ∈ {-2; -4; 2; -8}` để `3x+4 \vdots x+3`
