Đáp án + giải thích các bước giải:
`**) \sqrt{2015}-\sqrt{2013}`
`=((\sqrt{2015}-\sqrt{2013})(\sqrt{2015}+\sqrt{2013}))/(\sqrt{2015}+\sqrt{2013})`
`=(2015-2013)/(\sqrt{2015}+\sqrt{2013})`
`=2/(\sqrt{2015}+\sqrt{2013})`
`**) \sqrt{2014}-\sqrt{2012}`
`=((\sqrt{2014}-\sqrt{2012})(\sqrt{2014}+\sqrt{2012}))/(\sqrt{2014}+\sqrt{2012})`
`=(2014-2012)/(\sqrt{2014}+\sqrt{2012})`
`=2/(\sqrt{2014}+\sqrt{2012})`
Vì `2015>2014;2013>2012`
`->\sqrt{2015}+\sqrt{2013}>\sqrt{2014}+\sqrt{2012}`
`->2/(\sqrt{2015}+\sqrt{2013})<2/(\sqrt{2014}+\sqrt{2012})`
`->\sqrt{2015}-\sqrt{2013}< \sqrt{2014}-\sqrt{2012}`
