Đáp án: $n=2$
Giải thích các bước giải:
Để $\dfrac{14}{n}\in Z\to n\in U(14)$
$\to n\in\{1,2,7,14\}$
$\to n+1\in\{2,3,8,15\}$
$\to \dfrac{21}{n+1}\in\{\dfrac{21}{2},\dfrac{21}{3},\dfrac{21}{8},\dfrac{21}{15}\}$
$\to \dfrac{21}{n+1}\in\{\dfrac{21}{2},7,\dfrac{21}{8},\dfrac{7}{5}\}$
$\to$Để $\dfrac{21}{n+1}\in Z\to \dfrac{21}{n+1}=7\to n=2$