Biểu thức
`= (\sqrt{a} + \sqrt{b})/(2(\sqrt{a} - \sqrt{b})) - (\sqrt{a} - \sqrt{b})/(2(\sqrt{a} + \sqrt{b})) + (2b)/((\sqrt{a} - \sqrt{b})(\sqrt{a} + \sqrt{b})) - (2\sqrt{b})/(\sqrt{a} - \sqrt{b})`
`= ((\sqrt{a} + \sqrt{b})² - (\sqrt{a} - \sqrt{b})² + 4b - 4\sqrt{b}(\sqrt{a} + \sqrt{b}))/(2(\sqrt{a} - \sqrt{b})(\sqrt{a} + \sqrt{b}))`
`= (a + 2\sqrt{ab} + b - a + 2\sqrt{ab} - b + 4b - 4\sqrt{ab} - 4b)/(2(a - b))`
`= 0/(2(a - b))`
`= 0`
