The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.5282\\[1 em]x_2 &= -0.5974+0.5236i\\[1 em]x_3 &= -0.5974-0.5236i \end{aligned} $$Polynomial $ 3x^3+2x^2-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.