$$x^3 = 841$$
Answer
$$ \begin{matrix}x_1 = 9.43913 & x_2 = -4.71957+8.17453i & x_3 = -4.71957-8.17453i \end{matrix} $$
Explanation
$$ \begin{aligned} x^3 &= 841&& \text{move all terms to the left hand side } \\[1 em]x^3-841 &= 0&& \\[1 em] \end{aligned} $$
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