Giup minh rút gọn với, tks

a) ` \sqrt{3+\sqrt{5}} -\sqrt{3-\sqrt{5}}`

`=( \sqrt{2}\sqrt{3+\sqrt{5}} -\sqrt{2}\sqrt{3-\sqrt{5}})/(\sqrt{2})` 

`= ( \sqrt{6+2\sqrt{5}} -\sqrt{6-2\sqrt{5}})/(\sqrt{2})` 

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

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

`= (\sqrt{5} + 1 - \sqrt{5} +1)/(\sqrt{2})` (vì `\sqrt{5}+1>0` , `\sqrt{5}-1>0`)

`= 2/(\sqrt{2})`

`= \sqrt{2}`

b) ` \sqrt{(8+\sqrt{15})/2} - \sqrt{(8-\sqrt{15})/2} `

`=\sqrt{(2(8+\sqrt{15}))/4} - \sqrt{(2(8-\sqrt{15}))/4} `

`=( \sqrt{16+2\sqrt{15}})/2- (\sqrt{16-2\sqrt{15}})/2`

`= ( \sqrt{(\sqrt{15}+1)^2})/2- (\sqrt{(\sqrt{15}-1)^2})/2`

`= (|\sqrt{15}+1|-|\sqrt{15}-1|)/2`

`= (\sqrt{15}+1-\sqrt{15}+1)/2` (vì `\sqrt{15}+1>0` , `\sqrt{15}-1>0`)

`=2/2 =1`