$$2x^4-5x^3-2x^2+15x+15 = 0$$
Answer
$$ \begin{matrix}x_1 = -0.97276+0.45678i & x_2 = -0.97276-0.45678i & x_3 = 2.22276+1.24631i \\[1 em] x_4 = 2.22276-1.24631i & \\[1 em] \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas
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