$$-x^3-x^2+4x+8 = 0$$
Answer
$$ \begin{matrix}x_1 = 2.28428 & x_2 = -1.64214+0.89754i & x_3 = -1.64214-0.89754i \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
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Polynomial Equations Solver