Đáp án:
Giải thích các bước giải:
a) $3-n\vdots 2n+1\\\Leftrightarrow n-3\vdots 2n+1\\\Leftrightarrow 2n-6vdots 2n+1\\\Leftrightarrow 2n+1-7\vdots 2n+1\\\Leftrightarrow 7\vdots 2n+1\\\Leftrightarrow n\in \{\pm 1 ; \pm 7\}$
b) $n+1\vdots n^2-4\\\Leftrightarrow (n-1)(n+1)\vdots n^2-4\\\Leftrightarrow n^2-4+3\vdots n^2-4\\\Leftrightarrow 3\vdots n^2-4\\\Leftrightarrow n\in \{∅\}$