The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.428\\[1 em]x_2 &= -1.5141\\[1 em]x_3 &= 3.0861 \end{aligned} $$Polynomial $ x^3-2x^2-4x+2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.