\[3x^{4} + 8x² - 3 = 0\]
\[Пусть\ t = x^{2} \geq 0:\ \ \]
\[3t^{2} + 8t - 3 = 0\]
\[t_{1} + t_{2} = - \frac{8}{3};\ \ t_{1} \cdot t_{2} = - 1\]
\[\Longrightarrow t_{1} = - 3\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ t_{2} = \frac{1}{3}\]
\[x^{2} = - 3\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{\ x}^{2} = \frac{1}{3}\]
\[нет\ решения;\ x = \pm \sqrt{\frac{1}{3}} = \pm \frac{1}{\sqrt{3}}\]
\[Ответ:\ \pm \frac{1}{\sqrt{3}}.\]