The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.3781\\[1 em]x_2 &= -2.4243+1.6821i\\[1 em]x_3 &= -2.4243-1.6821i \end{aligned} $$Polynomial $ 17x^3+42x^2-48x-352 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.