The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.5487\\[1 em]x_2 &= -2.0747\\[1 em]x_3 &= 0.263+1.5558i\\[1 em]x_4 &= 0.263-1.5558i \end{aligned} $$Polynomial $ x^4-x^2+3x-8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.