The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.8299\\[1 em]x_2 &= 0.804\\[1 em]x_3 &= 0.4692+0.8539i\\[1 em]x_4 &= 0.4692-0.8539i\\[1 em]x_5 &= -0.6399+0.8984i\\[1 em]x_6 &= -0.6399-0.8984i\\[1 em]x_7 &= -1.5663+1.4454i\\[1 em]x_8 &= -1.5663-1.4454i \end{aligned} $$Polynomial $ 2x^8+7x^7+12x^6+5x^5+3x^4+2x^3+3x^2-5x-7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using Newton method.