Đáp án + Giải thích các bước giải:
`a//5n+9` $\vdots$ `n+4`
`⇒5(n+4)-11` $\vdots$ `n+4`
`⇒11` $\vdots$ `n+4`
`⇒n+4∈Ư(11)={±1;±11}`
`⇒n∈{-3;7;-5;-15}`
`b//3n+2` $\vdots$ `2n+3`
`⇒6n+4` $\vdots$ `2n+3`
`⇒3(2n+3)-5` $\vdots$ `2n+3`
`⇒5` $\vdots$ `2n+3`
`⇒2n+3∈Ư(5)={±1;±5}`
`⇒2n∈{-2;2;-4;-8}`
`⇒n∈{-1;1;-2;-4}`
`c//n^{2}+7` $\vdots$ `n+2`
`⇒(n^{2}+2n)-(2n+4)+11` $\vdots$ `n+2`
`⇒n(n+2)-2(n+2)+11` $\vdots$ `n+2`
`⇒(n+2)(n-2)+11` $\vdots$ `n+2`
`⇒11` $\vdots$ `n+2`
`⇒n+2∈Ư(11)={±1;±11}`
`⇒n∈{-1;9;-3;-13}`
