The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2i\\[1 em]x_2 &= -2i\\[1 em]x_3 &= -1+1.7321i\\[1 em]x_4 &= -1-1.7321i \end{aligned} $$Polynomial $ x^4+2x^3+8x^2+8x+16 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.