Đáp án:
`A = 3/(n + 1)`
`text{Để A nguyên}`
`-> 3 \vdots n + 1`
`-> n + 1 ∈ Ư (3) = {±1; ±3} (n ∈ ZZ)`
`text{Ta sẽ có :}`
\(\left\{ \begin{array}{l}n+1=1\\n+1=-1\\n+1=3\\n+1=-3\end{array} \right.\)
`⇔` \(\left\{ \begin{array}{l}n=0\\n=-2\\n=2\\n=-4\end{array} \right.\)
`text{Vậy n = (0;-2;2;-4) để A nguyên}`