$$20 = \frac{1}{2}(x+3)(x+5)x$$
Answer
$$ \begin{matrix}x_1 = 1.41326 & x_2 = -4.70663+2.48012i & x_3 = -4.70663-2.48012i \end{matrix} $$
Explanation
$$ \begin{aligned} 20 &= \frac{1}{2}(x+3)(x+5)x&& \text{multiply ALL terms by } \color{blue}{ 2 }. \\[1 em]2\cdot20 &= 2 \cdot \frac{1}{2}(x+3)(x+5)x&& \text{cancel out the denominators} \\[1 em]40 &= x^3+8x^2+15x&& \text{move all terms to the left hand side } \\[1 em]40-x^3-8x^2-15x &= 0&& \text{simplify left side} \\[1 em]-x^3-8x^2-15x+40 &= 0&& \\[1 em] \end{aligned} $$
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