$$(5x^3+x^2-4x+12)(x+3) = 0$$
Answer
$$ \begin{matrix}x_1 = -3 & x_2 = -1.61521 & x_3 = 0.70761+0.99255i \\[1 em] x_4 = 0.70761-0.99255i & \\[1 em] \end{matrix} $$
Explanation
$$ \begin{aligned} (5x^3+x^2-4x+12)(x+3) &= 0&& \text{simplify left side} \\[1 em]5x^4+16x^3-x^2+36 &= 0&& \\[1 em] \end{aligned} $$
This page was created using
Polynomial Equations Solver