The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.9311\\[1 em]x_2 &= -0.4656+1.5851i\\[1 em]x_3 &= -0.4656-1.5851i \end{aligned} $$Polynomial $ x^3-2x^2-8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.