`a)(3n+2)`$\vdots$`n-1`
`⇒[3(n-1)+5]`$\vdots$`n-1`
`⇒5`$\vdots$`n-1`
`⇒n-1∈Ư(5)={±1,±5}`
`⇒n∈{2,0,6,-4}`
`b)(3n+24)`$\vdots$`n-4`
`⇒[3(n-4)+36]`$\vdots$`n-4`
`⇒36`$\vdots$`n-4`
`⇒n-4∈Ư(36)={±1,±2,±3,±4,±6,±9,±12,±18,±36}`
`⇒n∈{5,3,6,2,7,1,8,0,10,-2,13,-5,16,-8,22,-14,40,-32}`
`c)(n^2+5)`$\vdots$`n+1`
`⇒ [(n^2-1)+6]` $\vdots$`n+1`
`⇒[(n-1)(n+1)+6]` $\vdots$`n+1`
`⇒6` $\vdots$`n+1`
`⇒n+1∈Ư(6)={±1,±2,±3,±6}`
`⇒n∈{0,-2,1,-3,2,-4,5,-7}`