The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.6263\\[1 em]x_2 &= -3.568\\[1 em]x_3 &= -0.0292+0.8298i\\[1 em]x_4 &= -0.0292-0.8298i \end{aligned} $$Polynomial $ x^4+2x^3-5x^2+x-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.