Question

Tìm nϵN :

a) n² + 2n + 7 chia hết cho n + 2

b) n² + 1 chia hết cho n-1

c) 12 - n chia hết cho 8 - n

 

Answer 1

a: \(\Leftrightarrow n\left(n+2\right)+7⋮n+2\)

\(\Leftrightarrow n+2\in\left\{1;-1;7;-7\right\}\)

hay \(n\in\left\{-1;-3;5;-9\right\}\)

b: \(\Leftrightarrow n^2-1+2⋮n-1\)

\(\Leftrightarrow n-1\in\left\{1;-1;2;-2\right\}\)

hay \(n\in\left\{2;0;3;-1\right\}\)

c: \(\Leftrightarrow n-12⋮n-8\)

\(\Leftrightarrow n-8-4⋮n-8\)

\(\Leftrightarrow n-8\in\left\{1;-1;2;-2;4;-4\right\}\)

hay \(n\in\left\{9;7;10;6;12;4\right\}\)