giúp tui nhé mng ơiiiiiiiiiiiii

`5)`

ĐK: `x ne +-\sqrt{2}`

`(x^2-2)/2=98/(x^2-2)`

`=> (x^2-2)^2=98.2`

`<=> (x^2-2)^2=196`

`<=> (x^2-2)^2=(+-14)^2`

`<=>`\(\left[ \begin{array}{l}x^2-2=14\\x^2-2=-14\end{array} \right.\) 

`<=>`\(\left[ \begin{array}{l}x^2=16\\x^2=-12 \text{ (vô lí)}\end{array} \right.\) 

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

`<=>`\(\left[ \begin{array}{l}x=4(tm)\\x=-4(tm)\end{array} \right.\) 

Vậy `xin {+-4}`