Bài 4:
` a) ` ` 3 \vdots n + 5 `
` => n + 5 ` ` ∈ ` ` Ư(3) = {± 1 ; ± 3} `
` => n ` ` ∈ ` ` {-6 ; 4 ; -8 ; -2} `
` b) ` ` -3n + 2 \vdots 2n + 1 `
` => -2.(-3n + 2) \vdots 2n + 1 `
` => 6n - 4 \vdots 2n + 1 `
` => 6n + 3 - 7 \vdots 2n + 1 `
Vì ` 6n + 3 \vdots 2n + 1 `
` => -7 \vdots 2n + 1 `
` => 2n + 1 ` ` ∈ ` ` Ư(-7) = {± 1 ; ± 7} `
` => 2n ` ` ∈ ` ` {-2 ; 0 ; -8 ; 6} `
` => n ` ` ∈ ` ` {-1 ; 0 ; -4 ; 3} `
