$$140x^6-56x^4+35x^2-25 = 0$$
Answer
$$ \begin{matrix}x_1 = -0.73752 & x_2 = 0.73752 & x_3 = 0.5005+0.56786i \\[1 em] x_4 = 0.5005-0.56786i & x_5 = -0.5005+0.56786i & x_6 = -0.5005-0.56786i \end{matrix} $$
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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