`a)\sqrt{3}(\sqrt{3}-1)`
`=3-\sqrt{3}`
`b)(\sqrt{5}-2)(\sqrt{5}+2)`
`=5-4`
`=1`
`c)(\sqrt{3}-2)²`
`=3-4\sqrt{3}+4`
`=7-4\sqrt{3}`
`d)(2\sqrt{5}+1)²`
`=20+4\sqrt{5}+1`
`=21+4\sqrt{5}`
`e)(\sqrt{3}-1)(\sqrt{3}+1)`
`=3-1`
`=2`
`f)(\sqrt{5}-2)(3+\sqrt{5})`
`=3\sqrt{5}+5-6-2\sqrt{5}`
`=\sqrt{5}-1`