$$x^8-256 = 0$$
Answer
$$ \begin{matrix}x_1 = 2 & x_2 = -2 & x_3 = 1.41421+1.41421i \\[1 em] x_4 = 1.41421-1.41421i & x_5 = -1.41421+1.41421i & x_6 = -1.41421-1.41421i \\[1 em] x_7 = 2i & x_8 = -2i \\[1 em] \end{matrix} $$
Explanation
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