The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.8897\\[1 em]x_2 &= 1.9448+1.6025i\\[1 em]x_3 &= 1.9448-1.6025i \end{aligned} $$Polynomial $ x^3-2x^2-x+12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.