The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.6975\\[1 em]x_2 &= -1.8556\\[1 em]x_3 &= 0.0791+1.78i\\[1 em]x_4 &= 0.0791-1.78i \end{aligned} $$Polynomial $ 2x^4+2x-20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.