$$x^6+17x^4+16x^2-100 = 0$$
Answer
$$ \begin{matrix}x_1 = 1.38381 & x_2 = -1.38381 & x_3 = 1.83205i \\[1 em] x_4 = -1.83205i & x_5 = 3.94443i & x_6 = -3.94443i \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using Newton method.
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