`9 - n vdots n - 3`
`=> n-9 vdots n-3`
`=> (n-3) -6 vdots n-3`
Mà `n-3 vdots n-3`
`=> 6 vdots n-3`
`=> n-3 inƯ(6)`
`2n + 7 vdots n+1`
`=> 2(n+1) +5 vdots n+1`
Mà `2(n+1) vdots n+1`
`=> 5 vdots n+1`
`=> n+1 inƯ(5)`
`3n + 7 vdots 2n + 1`
`=> 6n+14 vdots 2n + 1`
`=> 3(2n-1) +17 vdots 2n + 1`
Mà `3(2n-1) vdots 2n + 1`
`=> 17 vdots 2n + 1`
`=> 2n+1 inƯ(17)`
`n^2 + n + 17 vdots n + 1`
`=> n(n+1) +17 vdots n + 1`
Mà `n(n+1) vdots n + 1`
`=> 17 vdots n + 1`
`=> n+1 in Ư(17)`
`n^2 + 25 vdots n + 2`
`=>n.(n+2) -2(n+2) +29 vdots n + 2`
Mà `n.(n+2) vdots n + 2`
`2(n+2) vdots n + 2`
`=> 29 vdots n+2`
`=> n+2 in Ư (29)`
`3n^2+ 5 vdots n -1`
`=> 3n(n -1) + 3(n-1)+8 vdots n -1`
Mà `3n(n -1) vdots n -1`
`3(n-1) vdots n -1`
`=> 8 vdots n -1`
`=> n-1in Ư( 8 )`
`2)`
`|2x+1| - 19 = -7`
`=> |2x+1| =-7+19=12`
`=> 2x+1 = 12` hoặc `2x+1=-12`
`-28 -7. |-3x+15|= -70`
`=> 7. |-3x+15|=-28-(-70)=42`
`=> |-3x+15| =42:7=6`
`=> -3x+15=6` hoặc `-3x+15=-6`