Đáp án:
`(n + 1)/(n - 1)`
Đề `(n + 1)/(n - 1)` nguyên
`-> n + 1 \vdots n - 1`
`-> n - 1 + 2 \vdots n - 1`
Vì `n - 1 \vdots n - 1`
`-> 2 \vdots n - 1`
`-> n - 1 ∈ Ư (2) = {±1; ±2}`
`->` \(\left\{ \begin{array}{l}n-1=1\\n-1=-1\\n-1=2\\n-1=-2\end{array} \right.\)
`->` \(\left\{ \begin{array}{l}x=2\\n=0\\n=3\\n=-1\end{array} \right.\)
Vậy `n ∈ {2;0;3;-1}` để `(n + 1)/(n - 1)` nguyên
