Question

Giúp mik vs ạ mình đang cần ạ

Answer 1

`1)((sqrt{14}-sqrt7)/(1-sqrt2)+(sqrt{15}-sqrt5)/(1-sqrt3)):1/(sqrt7-sqrt5)`

`=((sqrt7(sqrt2-1))/(1-sqrt2)+(sqrt5(sqrt3-1))/(1-sqrt3):1/(sqrt7-sqrt5)`

`=(-sqrt7-sqrt5):1/(sqrt7-sqrt5)`

`=-(sqrt7+sqrt5).(sqrt7-sqrt5)`

`=-(7-5)`

`=-2`

`2)B=(2sqrtx-9)/(x-5sqrtx+6)-(sqrtx+3)/(sqrtx-2)-(2sqrtx+1)/(3-sqrtx)`

`=(2sqrtx-9-x+9+2x-3sqrtx-2)/(x-5sqrtx+6)`

`=(x-sqrtx-2)/(x-5sqrtx+6)`

`=((sqrtx-2)(sqrtx+1))/((sqrtx-2)(sqrtx-3))`

`=(sqrtx+1)/(sqrtx-3)`

`x=11+6sqrt2`

`=(3+sqrt2)^2`

`=>B=(4+2sqrt2)/(sqrt2)`

`=2+2sqrt2`

Answer 2

`3)5x^4+4x^2-1=0`

Đặt `t=x^2(t>=0)`

`pt<=>5t^2+4t-1=0`

`a-b+c=0`

`=>t_1=-1(l),t_2=1/5(tm)`

`<=>x=+-sqrt{1/5}`

Vậy `S={-sqrt{1/5},+sqrt{1/5}}`