The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.7976\\[1 em]x_2 &= 2.9279\\[1 em]x_3 &= 0.4348+1.446i\\[1 em]x_4 &= 0.4348-1.446i \end{aligned} $$Polynomial $ x^4-2x^3-2x^2+2x-12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.