The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.4818\\[1 em]x_2 &= -0.8251\\[1 em]x_3 &= 0.1717+1.5767i\\[1 em]x_4 &= 0.1717-1.5767i \end{aligned} $$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.