tính rút gọn giúp mk vs nha, mk cảm ơn

`1)`

`A={4}/{sqrt{5}+1}-sqrt{9-4sqrt{5}}`

`={4(sqrt{5}-1)}/{(sqrt{5}-1)(sqrt{5}+1)}-sqrt{5-4sqrt{5}+4}`

`={4(sqrt{5}-1)}/{(sqrt{5})^2-1^2}-sqrt{(sqrt{5})^2-2.sqrt{5}.2+2^2}`

`={4(sqrt{5}-1)}/{4}-sqrt{(sqrt{5}-2)^2}`

`=sqrt{5}-1-|sqrt{5}-2|`

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

`=1` 

`2)`

`a)`

`A={sqrt{x}-7}/{x-5sqrt{x}+6}+{sqrt{x}+3}/{2-sqrt{x}}+{2sqrt{x}+1}/{sqrt{x}-3}`

Điều kiện : `x>=0;x\ne4;x\ne9`

`={sqrt{x}-7}/{(sqrt{x}-3)(sqrt{x}-2)}-{sqrt{x}+3}/{sqrt{x}-2}+{2sqrt{x}+1}/{sqrt{x}-3}`

`={sqrt{x}-7-(sqrt{x}+3)(sqrt{x}-3)+(2sqrt{x}+1)(sqrt{x}-2)}/{(sqrt{x}-3)(sqrt{x}-2)}`

`={sqrt{x}-7-x+9+2x-3sqrt{x}-2}/{(sqrt{x}-3)(sqrt{x}-2)}`

`={sqrt{x}(sqrt{x}-2)}/{(sqrt{x}-3)(sqrt{x}-2)}`

`={sqrt{x}}/{sqrt{x}-3}`

`b)`

Ta có : `x=3-2sqrt{2}`

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

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

`=(sqrt{2}-1)^2` (thỏa điều kiện )

Thay vào `A :`

`=>A={sqrt{(sqrt{2}-1)^2}}/{sqrt{(sqrt{2}-1)^2}-3}`

`={|sqrt{2}-1|}/{|sqrt{2}-1|-3}`

`={sqrt{2}-1}/{sqrt{2}-4}`

`={2-3sqrt{2}}/{14}`

Vậy `A={2-3sqrt{2}}/{14}` khi `x=3-2sqrt{2}`