Đáp án+Giải thích các bước giải:
`b) (2 - \sqrt{2})(-5\sqrt{2}) - (3\sqrt{2} - 5)²`
`= 2 . (-5\sqrt{2}) - \sqrt{2}(-5\sqrt{2}) - [(3\sqrt{2})² - 2 . 5 . 3\sqrt{2} + 5²]`
`= - 10\sqrt{2} + 5 . 2 - (18 - 30\sqrt{2} + 25)`
`= - 10\sqrt{2} + 10 - 18 + 30\sqrt{2} - 25`
`= 20\sqrt{2} - 33`
`c) \frac{1}{\sqrt{5} - \sqrt{7}} + \frac{\sqrt{10} - 2\sqrt{14}}{\sqrt{2}}`
`= \frac{\sqrt{5} + \sqrt{7}}{(\sqrt{5} + \sqrt{7})(\sqrt{5} - \sqrt{7})} + \frac{\sqrt{2}(\sqrt{5} - 2\sqrt{7})}{\sqrt{2}}`
`= \frac{\sqrt{5} + \sqrt{7}}{5 - 7} + (\sqrt{5} - 2\sqrt{7})`
`= \frac{\sqrt{5} + \sqrt{7}}{-2} + \frac{- 2\sqrt{5} + 4\sqrt{7}}{-2}`
`= \frac{\sqrt{5} + \sqrt{7} - 2\sqrt{5} + 4\sqrt{7}}{-2}`
`= \frac{5\sqrt{7} - \sqrt{5}}{-2}`
`= \frac{\sqrt{5} - 5\sqrt{7}}{2}`
