The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.272\\[1 em]x_2 &= -1.272\\[1 em]x_3 &= 0.7862i\\[1 em]x_4 &= -0.7862i \end{aligned} $$Polynomial $ x^4-x^2-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.