a) Ta có : \(n-1\inƯ\left(15\right)=\left\{\pm1;\pm3;\pm5;\pm15\right\}\)
\(\Rightarrow n\in\left\{0;2;-2;4;-4;6;-14;16\right\}\)
b) Ta có : 2n-1\(⋮\)n-3
\(\Rightarrow\)2n-6+5\(⋮\)n-3
\(\Rightarrow\)2(n-3)+5\(⋮\)n-3
\(\Rightarrow n-3\inƯ\left(5\right)=\left\{\pm1;\pm5\right\}\)
\(\Rightarrow n\in\left\{4;2;8-2\right\}\)