$$x^6+2x^4+x^2-1 = 0$$
Answer
$$ \begin{matrix}x_1 = 0.68233 & x_2 = -0.68233 & x_3 = -0.34116+1.16154i \\[1 em] x_4 = -0.34116-1.16154i & x_5 = 0.34116+1.16154i & x_6 = 0.34116-1.16154i \end{matrix} $$
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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