`#khanhly2949`

`e,`

`x^2-x-9=0`

`<=>x^2-2 . x . 1/2+1/4-37/4=0`

`<=>(x-1/2)^2=37/4`

`th_1 : (x-1/2)^2=(\sqrt{37})/2`

`<=>x=(1+\sqrt{37})/2`

`th_2 : (x-1/2)^2=(-\sqrt{37})/2`

`<=>x=(1-\sqrt{37})/2`

Vậy `S={(1+\sqrt{37})/2;(1-\sqrt{37})/2}`

`g,`

`x^2-2\sqrt{2}x-5=0`

`<=>x^2-2\sqrt{2}x+2-7=0`

`<=>(x-\sqrt{2})^2=7`

`th_1 : (x-\sqrt{2})=(\sqrt{7})^2`

`<=> x-\sqrt{2}=\sqrt{7}`

`<=>x=\sqrt{7}+\sqrt{2}`

`th_2 : (x-\sqrt{2})=(-\sqrt{7})^2`

`<=> x-\sqrt{2}=-\sqrt{7}`

`<=>x=\sqrt{2}-\sqrt{7}`

Vậy `S={\sqrt{7}+\sqrt{2};\sqrt{2}-\sqrt{7}}`