a: \(\Leftrightarrow n^2-9+3⋮n-3\)
\(\Leftrightarrow n-3\in\left\{1;-1;3;-3\right\}\)
hay \(n\in\left\{4;2;6;0\right\}\)
b: \(-2n+3⋮3n+2\)
\(\Leftrightarrow-6n+9⋮3n+2\)
\(\Leftrightarrow-6n-4+13⋮3n+2\)
\(\Leftrightarrow3n+2\in\left\{1;-1;13;-13\right\}\)
hay \(n\in\left\{-1;-5\right\}\)