\[x^{6} + 3x^{4} - x^{2} - 3 = 0\]
\[x^{4}\left( x^{2} + 3 \right) - \left( x^{2} + 3 \right) = 0\]
\[\left( x^{2} + 3 \right)\left( x^{4} - 1 \right) = 0\]
\[x^{2} = - 3\ \ \ \ \ \ \ \ \ \ \ \ \ x^{4} = 1\]
\[нет\ корней\ \ \ \ \ \ x = \pm 1\]
\[Ответ:\ \ x = \pm 1.\]