The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.5249\\[1 em]x_2 &= 1.4902\\[1 em]x_3 &= -1.0076+0.5131i\\[1 em]x_4 &= -1.0076-0.5131i \end{aligned} $$Polynomial $ x^4-2x^2-x+1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.