Giải thích các bước :

`\sqrt{6 + 2\sqrt{5}} - \sqrt{6 - 2\sqrt{5}}`

`= \sqrt{5 + 2\sqrt{5} + 1} - \sqrt{5 - 2\sqrt{5} + 1}`

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

`= |\sqrt{5} + 1| - |\sqrt{5} - 1|`

`= \sqrt{5} + 1 - \sqrt{5} + 1`

`= 2`

`\sqrt{11 + 6\sqrt{2}} - \sqrt{11 - 6\sqrt{2}}`

`= \sqrt{9 + 6\sqrt{2} + 2} - \sqrt{9 - 6\sqrt{2} + 2}`

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

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

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

`= 2\sqrt{2}`

Mình không biết đề như nào :

______________________________________

`a)`

`sqrt6+2sqrt5-sqrt6-2sqrt5`

`=sqrt6 -sqrt6 +2sqrt5 -sqrt5`

`=0`

`b)` `sqrt11+6sqrt2 -sqrt11-6sqrt2`

`=sqrt11-sqrt11+6sqrt2-6sqrt2`

`=0`

____________________________________________

`a)`

`sqrt{6+2sqrt5}-{sqrt6-2sqrt5}`

`=sqrt{5+2sqrt5+1}-sqrt{5-2sqrt5+1}`

`=sqrt{(sqrt5)^2+2*sqrt5*1+1^2}-sqrt{(sqrt5)^2-2*sqrt5*1+1^2}`

`=sqrt{(sqrt5+1)^2}-sqrt{(sqrt5-1)^2}`

`=|sqrt5+1|-|sqrt5-1|`

`=sqrt5+1-sqrt5+1` `(Vì ` `sqrt5+1>0` `;` `sqrt5-1>0` `)`

`=2`

`b)`

`sqrt{11+6sqrt2}-sqrt{11-6sqrt2}`

`=sqrt{9+6sqrt2+2}-sqrt{9-6sqrt2+2}`

`=sqrt{3^2+2*3*sqrt2+(sqrt2)^2}-sqrt{3^2-2*3*sqrt2+(sqrt2)^2}`

`=sqrt{(3+sqrt2)^2}-sqrt{(3-sqrt2)^2}`

`=|3+sqrt2|-|3-sqrt2|`

`=3+sqrt2-3+sqrt2` `(Vì ` `3+sqrt2>0` `;` `3-sqrt2>0` `)`

`=2sqrt2`