`x + 2 . (sqrt{2x})^2 + 2x^3 = 0`

`<=> x + 2 . 2x + 2x^3 = 0`

`<=> x + 4x + 2x^3 = 0`

`<=> 5x + 2x^3 = 0`

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

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

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

Vậy `x = 0`