$6x^4+5x^2+1=0$
⇔ $2x^2.(3x^2-1)-3x^2+1=0$
⇔ $(3x^2-1)(2x^2-1)=0$
⇔ \(\left[ \begin{array}{l}3x^2-1=0\\2x^2-1=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x^2=\frac{1}{3}\\x^2=\frac{1}{2}\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=±\frac{\sqrt[]{3}}{3}\\x=±\frac{\sqrt[]{2}}{2}\end{array} \right.\)
Vậy $S=${$±\frac{\sqrt[]{3}}{3};±\frac{\sqrt[]{2}}{2}$}
