Смотри...............................

Возьмём левую часть и преобразуем

[tex] {(x - 1)}^{3} - 9(x - 1) = (x - 1)( {(x - 1)}^{2} - 9) = \\ \\ = (x - 1)((x - 1 - 3)(x - 1 + 3)) = (x - 1)(x - 4)(x + 2) \\ \\ \\ (x - 1)(x - 4)(x + 2) = (x - 1)(x - 4)(x + 2)[/tex]