The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.7913\\[1 em]x_2 &= -1.5616\\[1 em]x_3 &= 2.5616\\[1 em]x_4 &= -2.7913 \end{aligned} $$Polynomial $ x^4-10x^2+x+20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.