$$x^4+8x^3-9x+9 = 0$$
Answer
$$ \begin{matrix}x_1 = -1.51763 & x_2 = -7.83466 & x_3 = 0.67615+0.5475i \\[1 em] x_4 = 0.67615-0.5475i & \\[1 em] \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas
This page was created using
Polynomial Equations Solver