The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.1964\\[1 em]x_2 &= -0.9315+1.1667i\\[1 em]x_3 &= -0.9315-1.1667i \end{aligned} $$Polynomial $ -3x^3-2x^2+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.