$$r^3-7r^2+7r-7 = 0$$
Answer
$$ \begin{matrix}r_1 = 6.0319 & r_2 = 0.48405+0.96239i & r_3 = 0.48405-0.96239i \end{matrix} $$
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