Question

Giup voi a

Answer 1

`a)(n+2)^2-(n-2)^2`

`=(n+2-n+2)(n+2+n-2)`

`=4.2n=8n \vdots 8 AA n in ZZ`

    `->đpcm`

`b)(n+7)^2-(n-5)^2`

`=(n+7-n+5)(n+7+n-5)`

`=12.(2n+2)=24(n+1) \vdots 24 AA n in ZZ`

   `->đpcm`

Answer 2

`a, = n^2 + 4n + 4 - n^2 + 4n - 4`

`= 8n vdots 8 ( dpcm )`.

`b, = n^2 + 14n + 49 - n^2 + 10n - 25`

`= 24n -24`.

`= 24(n-1) vdots 24`.