`a) n+9` $\vdots$ `n+2`
`=> n+2+7` $\vdots$ `n+2`
Mà `n+2` $\vdots$ `n+2`
`=> 7` $\vdots$ `n+2`
`=> n+2 ∈ Ư(7)={1; 7}`
`=> n = 5`
`b) 4n+11` $\vdots$ `2n+1`
`=> 2(2n+1)+9` $\vdots$ `2n+1`
Mà `2(2n+1`) $\vdots$ `2n+1`
`=> 9` $\vdots$ `2n+1`
`=> 2n+1 ∈ Ư(9)={1; 3; 9}`
`=> 2n ∈ {0; 2; 8}`
`=> n ∈ {0; 1; 4}`
`c)2n+16` $\vdots$ `3-n`
`=> 2n+16` $\vdots$ `n-3`
`=> 2(n-3)+22` $\vdots$ `n-3`
Mà `2(n-3)` $\vdots$ `n-3`
`=> 22` $\vdots$ `n-3`
`=> n-3 ∈ Ư(22)={1; 2; 11; 22}`
`=> n ∈ {3; 5; 14; 25}`
