The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.268\\[1 em]x_2 &= -0.4142\\[1 em]x_3 &= 2.4142\\[1 em]x_4 &= 3.7321 \end{aligned} $$Polynomial $ x^4-6x^3+8x^2+2x-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.