Jup mik voi ahhhh!!!!!!!!!!!!

`c)n^2+4vdots2n+1`

`<=>4.(n^2+4)vdots2n+1`

`<=>4n^2+16vdots2n+1`

`<=>4n^2-1+17vdots2n+1`

`<=>(2n-1)(2n+1)+17vdots2n+1`

`=>17vdots2n+1`

`=>2n+1∈Ư_17={1,17,-1,-17}`

`=>2n∈{0,16,-2,-18}`

`=>n∈{0,8,-1,-9}`

`d)n^3+2nvdots3n-1`

`<=>27n^3+54vdots3n-1`

`<=>(3n)^3-1+55vdots3n-1`

`<=>(3n-1)(9n^2+3n+1)+55vdots3n-1`

`=>55vdots3n-1`

`=>3n-1∈Ư_55={1,5,11,55,-1,-5,-11,-55}`

`=>3n∈{2,6,12,56,0,-4,-10,-54}`

`=>n∈{2,4,0,-18}`

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