\(a\).
Ta có:
\(n+7⋮n\Rightarrow7⋮n\)
(Do \(n⋮n\) )
\(\Rightarrow n\inƯ\left(7\right)\Rightarrow n\in\left\{1;7\right\}\)
(Do \(n\in N\) )
b.
Ta có:
\(n+11⋮n+9\Rightarrow\left(n+9\right)+2⋮n+9\Rightarrow2⋮n+9\Rightarrow n+9\inƯ\left(2\right)\Rightarrow n+9\in\left\{\pm1;\pm2\right\}\)
\(\Rightarrow n\in\left\{-8;-7;-10;-11\right\}\)
Do n thuộc N
=>\(n\in\left\{\varnothing\right\}\)
c.Ta có:
\(2n+13⋮n+3\Rightarrow\left(2n+6\right)+7⋮n+3\Rightarrow7⋮n+3\Rightarrow n+3\inƯ\left(7\right)\)
(Do \(2n+6⋮n+3\) )
\(\Rightarrow n+3\in\left\{\pm1;\pm7\right\}\Rightarrow n\in\left\{4;-2;-4;-10\right\}\)
Do \(n\in N\Rightarrow n=4\)
