The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.79\\[1 em]x_2 &= -2.79\\[1 em]x_3 &= -12.4986\\[1 em]x_4 &= 12.4986 \end{aligned} $$Polynomial $ x^4-164x^2+1216 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.