х ≠ - 3

[tex] \frac{ {x}^{3} - {x}^{2} - 12x }{x + 3} = 0 \\ {x}^{3} - {x}^{2} - 12x = 0 \\ x(x {}^{2} - x - 12) = 0 \\ x_{3} = 0[/tex]

По теореме Виета:

[tex]{x}^{2} + bx + c = 0 \\ x _{1} + x_{2} = - b \\ x _{1} x_{2} = c[/tex]

[tex] {x}^{2} - x - 12 = 0 \\ x_{1} + x_{2} = 1 \\ x_{1} x_{2} = - 12 \\ x_{1} = - 3\\ x_{2} = 4[/tex]