The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -3.5063\\[1 em]x_2 &= 0.7532+1.3093i\\[1 em]x_3 &= 0.7532-1.3093i \end{aligned} $$Polynomial $ x^3+2x^2-3x+8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.