x^4 - 4x^2 -5 = 0 √x-1=3 √x+4=x-2 cuuuuuuuuuuu

Giải thích các bước giải+Đáp án:

 `x^4-4x^2-5=0`

`<=>x^4-5x^2+x^2-5=0`

`<=>x^2(x^2-5)+(x^2-5)=0`

`<=>(x^2+1)(x^2-5)=0`

`<=>`\(\left[ \begin{array}{l}x^2+1=0\\x^2-5=0\end{array} \right.\) 

`<=>`\(\left[ \begin{array}{l}x^2=-1 \text{(Vô lí)}\\x^2=5\end{array} \right.\) 

`<=>`\(\left[ \begin{array}{l}x=\sqrt5\\x=-\sqrt5\end{array} \right.\) 

Vậy: `S={\sqrt5;-\sqrt5}`

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`\sqrt{x-1}=3`

`<=>x-1=9`

`<=>x=10`

Vậy: `S={10}`

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`\sqrt{x+4}=x-2`  `(x>=2)`

`<=>x+4=(x-2)^2`

`<=>x+4=x^2-2x+4`

`<=>x^2-2x+4-x-4=0`

`<=>x^2-3x=0`

`<=>x(x-3)=0`

`<=>`\(\left[ \begin{array}{l}x=0\\x-3=0\end{array} \right.\)

`<=>`\(\left[ \begin{array}{l}x=0(KTM)\\x=3\end{array} \right.\)

Vậy: `S={3}`