$$4x^3+15x^2+16x+6 = 0$$
Answer
$$ \begin{matrix}x_1 = -2.28858 & x_2 = -0.73071+0.34856i & x_3 = -0.73071-0.34856i \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
This page was created using
Polynomial Equations Solver