The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.534+0.4994i\\[1 em]x_2 &= 0.534-0.4994i\\[1 em]x_3 &= -0.534+0.4994i\\[1 em]x_4 &= -0.534-0.4994i \end{aligned} $$Polynomial $ 14x^4-x^2+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.