a)
`5/(\sqrt{5})`
`=(5. \sqrt{5})/( \sqrt{5}.\sqrt{5})`
`=(5\sqrt{5})/5`
b)
`5/(\sqrt{2+\sqrt{3}})`
`=(5.\sqrt{2-\sqrt{3}})/((\sqrt{2+\sqrt{3}}) . (\sqrt{2-\sqrt{3}}))`
`=(5.\sqrt{2-\sqrt{3}})/(\sqrt{(2+\sqrt{3})(\sqrt{2}-\sqrt{3})`
`=(5.\sqrt{2-\sqrt{3}})/\sqrt{4-3}`
`=(5.\sqrt{2-\sqrt{3}})/1`
`=5.\sqrt{2-\sqrt{3}}`