The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.5209\\[1 em]x_2 &= -0.5209\\[1 em]x_3 &= 1.1085\\[1 em]x_4 &= -1.1085 \end{aligned} $$Polynomial $ 6x^4-9x^2+2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.