The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.2852\\[1 em]x_2 &= -0.3301+0.5739i\\[1 em]x_3 &= -0.3301-0.5739i \end{aligned} $$Polynomial $ 8x^3+3x^2+2x-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.