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.