a: =>n-1+4 chia hết cho n-1
=>\(n-1\in\left\{1;-1;2;-2;4;-4\right\}\)
hay \(n\in\left\{2;0;3;-1;5;-3\right\}\)
b: =>2n+4-5 chia hết cho n+2
=>\(n+2\in\left\{1;-1;5;-5\right\}\)
hay \(n\in\left\{-1;-3;3;-7\right\}\)
c: =>2n-6 chiahết cho 2n-3
=>\(2n-3\in\left\{1;-1;3;-3\right\}\)
hay \(n\in\left\{2;1;3;0\right\}\)