The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.9471\\[1 em]x_2 &= 1.9471\\[1 em]x_3 &= 0.8895i\\[1 em]x_4 &= -0.8895i \end{aligned} $$Polynomial $ x^4-3x^2-3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.