`1)` `x^2+2`
`=x^2+3-1`
`=(\sqrt{x^2+3})^2-1^2`
`=(\sqrt{x^2+3}-1)(\sqrt{x^2+3}+1)`
$\\$
`2)` `x^2+3`
`=x^2+4-1`
`=(\sqrt{x^2+4})^2-1^2`
`=(\sqrt{x^2+4}-1)(\sqrt{x^2+4}+1)`
$\\$
`3)` `x^2+5`
`=x^2+6-1`
`=(\sqrt{x^2+6})^2-1^2`
`=(\sqrt{x^2+6}-1)(\sqrt{x^2+6}+1)`
$\\$
`4)` `x^2-2`
`=x^2-(\sqrt{2})^2`
`=(x-\sqrt{2})(x+\sqrt{2})`