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Bài `1:`

a) `2\sqrt{72} - 1/2\sqrt{32} + 3\sqrt{50}`

`= 2\sqrt{36  . 2} - 1/2\sqrt{16 . 2} + 3\sqrt{25 . 2}`

`= 12\sqrt{2} - 2\sqrt{2} + 15\sqrt{2}`

`= 25\sqrt{2}`

b) `\sqrt{3}(\sqrt{3} + 1) + (2 - \sqrt{3})^2 + \sqrt{(1 - \sqrt{3})^2}` `

`= 3 + \sqrt{3} + 4 - 4\sqrt{3} + 3 + |1 - \sqrt{3}|`

`= 7 - 3\sqrt{3} + \sqrt{3} - 1`

`= 6 - 2\sqrt{3}`

c) `(\sqrt{10} - \sqrt{2})/(\sqrt{5} - 1) - 7/\sqrt{7} + 5/(\sqrt{7} - \sqrt{2})`

`= (\sqrt{2}(\sqrt{5} - 1)/(\sqrt{5} - 1) - \sqrt{7} + (5(\sqrt{7} + \sqrt{2}))/(7 - 2)`

`= \sqrt{2} - \sqrt{7} + \sqrt{7} + \sqrt{2}`

`= 2\sqrt{2}`

d) `cos^2 20^o - cot28^o . cot62^o + sin55^o - cos35^o + cos^2 70^o`

`= cos^2 20^o - cot28^o . tan28^o + sin55^o - sin55^o + sin^2 20^o`

`= cos^2 20^o + sin^2 20^o - 1`

`= 1 - 1`

`= 0`