$$-160x^6+240x^{12}-300 = 0$$
Answer
$$ \begin{matrix}x_1 = 1.06991 & x_2 = -1.06991 & x_3 = -0.84011+0.48504i \\[1 em] x_4 = -0.84011-0.48504i & x_5 = 0.84011+0.48504i & x_6 = 0.84011-0.48504i \\[1 em] x_7 = 0.53496+0.92657i & x_8 = 0.53496-0.92657i & x_9 = -0.53496+0.92657i \\[1 em] x_10 = -0.53496-0.92657i & x_11 = 0.97007i & x_12 = -0.97007i \end{matrix} $$
Explanation
$$ \begin{aligned} -160x^6+240x^{12}-300 &= 0&& \text{simplify left side} \\[1 em]240x^{12}-160x^6-300 &= 0&& \\[1 em] \end{aligned} $$
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using Newton method.
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