The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.8527\\[1 em]x_2 &= -2.4349\\[1 em]x_3 &= 1.1438+0.3694i\\[1 em]x_4 &= 1.1438-0.3694i \end{aligned} $$Polynomial $ -x^4-x^3+4x^2-3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.