The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.7937\\[1 em]x_2 &= -0.3969+0.6874i\\[1 em]x_3 &= -0.3969-0.6874i \end{aligned} $$Polynomial $ -4x^3+2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.