`(\sqrt{x-2\sqrt{2x-4}})/\sqrt{2}` `(x>=6)`

`=(\sqrt{x-2\sqrt{2x-4}}*\sqrt{2})/(\sqrt{2}*\sqrt{2)`

`=(\sqrt{2x-4\sqrt{2x-4}})/2`

`=(\sqrt{(2x-4)-4\sqrt{2x-4}+4})/2`

`=(\sqrt{(\sqrt{2x-4}-2)^2})/2`

`=|\sqrt{2x-4}-2|/2`

`=(\sqrt{2x-4}-2)/2`

`=(\sqrt{2x-4})/2-1`

~~~~~

Công thức:

`a^2-2ab+b^2=(a-b)^2`