The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.8026\\[1 em]x_2 &= -0.7763+0.8021i\\[1 em]x_3 &= -0.7763-0.8021i \end{aligned} $$Polynomial $ 4x^3+3x^2-4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.