\(\Rightarrow6a-1⋮a-2\)
\(\Rightarrow\left(6a-12\right)+13\)\(⋮a-2\)
\(\Rightarrow6\left(a-2\right)+13\)\(⋮a-2\)
Vì \(a-2\)\(⋮a-2\)
nên \(6\left(a-2\right)\)\(⋮a-2\)
\(\Rightarrow13\)\(⋮a-2\)
\(\Rightarrow a-2\in\left\{13;-13\right\}\)
\(\Rightarrow a\in\left\{15;-11\right\}\)
Vậy \(a\in\left\{15;-11\right\}\)