The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.7772+0.3979i\\[1 em]x_2 &= 1.7772-0.3979i\\[1 em]x_3 &= -1.7772+0.3979i\\[1 em]x_4 &= -1.7772-0.3979i \end{aligned} $$Polynomial $ x^4-6x^2+11 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.