`c) 2\sqrt{16/3} - 3\sqrt{1/27} - 6\sqrt{4/75}`

`= 2 . 4\sqrt{1/3} - 3\sqrt{1/9 . 1/3} - 6\sqrt{4/25 . 1/3}`

`= 8\sqrt{1/3} - 3 . 1/3\sqrt{1/3} - 6 . 2/5\sqrt{1/3}`

`= 8\sqrt{1/3} - \sqrt{1/3} - 12/5\sqrt{1/3}`

`= \sqrt{1/3}( 8 - 1 - 12/5 )`

`23/5\sqrt{1/3}`

`= ( 23\sqrt{3})/15`

`d) ( 7\sqrt{75} + 2\sqrt{27} - 3\sqrt{48} ) : \sqrt{3}`

`= ( 7\sqrt{25 . 3} + 2\sqrt{9 . 3} - 3\sqrt{16. 3} ) : \sqrt{3}`

`= \sqrt{3} . ( 7\sqrt{25} + 2\sqrt{9} - 3\sqrt{16} ) : \sqrt{3}`

`= 7 . 5 + 2 . 3 - 3 . 4`

`= 35 + 6 - 12`

`= 41 - 12`

`= 29`

`c) \sqrt{4 + 2\sqrt{3}} + \sqrt{7 - 4\sqrt{3}}`

`= \sqrt{3 + 2\sqrt{3} + 1} + \sqrt{4 - 4\sqrt{3} + 3}`

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

`= | \sqrt{3} + 1 | + | 2 - \sqrt{3} |`

`= \sqrt{3} + 1 + 2 - \sqrt{3}  ( do  2 = \sqrt{4} > \sqrt{3} )`

`= 3`

`H = 2\sqrt{9a - 9} - 8\sqrt{( a - 1 )/4} - \sqrt{a - 1}` với `a >= 0`

`H = 2\sqrt{9( a - 1 )} - 8\sqrt{1/4 . ( a - 1 )} - \sqrt{a - 1}`

`H = 2 . 3\sqrt{a - 1} - 8 . 1/2\sqrt{a - 1} - \sqrt{a - 1}`

`H = 6\sqrt{a- 1} - 4\sqrt{a - 1} - \sqrt{a - 1}`

`H = \sqrt{a - 1}`

_________________

`K = \sqrt{ab} - b\sqrt{a/b} + 2/b\sqrt{ab^3}` với `a < 0 ; b < 0`

`K = \sqrt{ab} - ( -\sqrt{b})^2 . \sqrt{a} . 1/\sqrt{b} + 2/b . | b |\sqrt{ab}`

`K = \sqrt{ab} + \sqrt{ab}  - 2/b . b\sqrt{ab}`

`K = 2\sqrt{ab} - 2\sqrt{ab}`

`K = 0`