$$-x^3+9x^2-21x+12 = 0$$
Answer
$$ \begin{matrix}x_1 = 0.8549 & x_2 = 2.47602 & x_3 = 5.66908 \end{matrix} $$
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