$$(x+1)(x+2)(x-2) = 15$$
Answer
$$ \begin{matrix}x_1 = 2.81614 & x_2 = -1.90807+1.76241i & x_3 = -1.90807-1.76241i \end{matrix} $$
Explanation
$$ \begin{aligned} (x+1)(x+2)(x-2) &= 15&& \text{simplify left side} \\[1 em](x^2+2x+x+2)(x-2) &= 15&& \\[1 em](x^2+3x+2)(x-2) &= 15&& \\[1 em]x^3-2x^2+3x^2-6x+2x-4 &= 15&& \\[1 em]x^3+x^2-4x-4 &= 15&& \text{move all terms to the left hand side } \\[1 em]x^3+x^2-4x-4-15 &= 0&& \text{simplify left side} \\[1 em]x^3+x^2-4x-19 &= 0&& \\[1 em] \end{aligned} $$
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