`a)n+7 \vdots n+2`
`=>(n+7)-(n+2) \vdots n+2`
`=>[(n-n)+(7-2)] \vdots n+2`
`=>[0+5] \vdots n+2`
`=>5 \vdots n+2`
`=>n+2∈(Ư)5={-1;1;-5;5}`
`=>n∈{(-1)-2;1-2;(-5)-2;5-2}`
`=>n∈{-3;-1;-7;3}`
`b)2n+3 \vdots 2n-2`
`=>[(2n+3)-(2n-2)] \vdots 2n-2`
`=>[(2n-2n)+(3+2)] \vdots 2n-2`
`=>[0+5] \vdots 2n-2`
`=>5 \vdots 2n-2`
`=>2n-2∈(Ư)5={-1;1;-5;5}`
`=>2n∈{1;3;-3;7}`
`=>n \ne 0`
`c)2n+1 \vdots 2-3n`
`=>6(2n+1) \vdots 2-3n`
`=>6n+1 \vdots 2-3n`
`=>6n-3n+1 \vdots 2-3n`
`=>3(2-3n )+2 \vdots 2n-3`
`=>2 \vdots 2n-3`
`=>2n-3∈(Ư)2={1;2;-1;-2}`
`=> n \ne 0`
