The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.659\\[1 em]x_2 &= -1.3295+0.8023i\\[1 em]x_3 &= -1.3295-0.8023i \end{aligned} $$Polynomial $ x^3+x^2-2x-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.