$$-x^3+x^2-2x+20 = 0$$
Answer
$$ \begin{matrix}x_1 = 2.81438 & x_2 = -0.90719+2.50666i & x_3 = -0.90719-2.50666i \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
This page was created using
Polynomial Equations Solver