Question

Bài 5: Tìm các số tự nhiên n sao cho:
a) 15 ⋮ n+2        b) 21 ⋮ 2n + 3             c) n + 2 ⋮ n-1             d) 2n + 9 ⋮ n +3               

e) n + 4 ⋮ n + 1

Answer 1

a: \(\Leftrightarrow n+2\in\left\{3;5;15\right\}\)

hay \(n\in\left\{1;3;13\right\}\)

b: \(\Leftrightarrow2n+3\in\left\{3;7;21\right\}\)

hay \(n\in\left\{0;2;9\right\}\)

c: =>n-1+3 chia hết cho n-1

\(\Leftrightarrow n-1\in\left\{1;-1;3;-3\right\}\)

hay \(n\in\left\{2;0;4;-2\right\}\)

d: =>2n+6+3 chia hết cho n+3

\(\Leftrightarrow n+3\in\left\{1;-1;3;-3\right\}\)

hay \(n\in\left\{-2;-4;0;-6\right\}\)

e: =>3 chia hết cho n+1

\(\Leftrightarrow n+1\in\left\{1;-1;3;-3\right\}\)

hay \(n\in\left\{0;-2;2;-4\right\}\)