$1,(\sqrt{3}-1)(\sqrt{3}+1)$
`=\sqrt{3}^2-1^2`
`=3-1`
`=2`
`2,(2+\sqrt{3})(2-\sqrt{3})`
`2^2-\sqrt{3}^2`
`=4-3`
`=1`
`3,(\sqrt{5}+2\sqrt{2})(\sqrt{5}-2\sqrt{2})`
`=\sqrt{5}^2+(2\sqrt{2})^2`
`=5-8`
`=-3`
`4,(2+\sqrt{3})(2-\sqrt{3})`
`=2^2-\sqrt{3}^2`
`=4-3`
`=1`