Егор Преобразуем 2 * (x^2 - 1) - (x - 1) = 2 * (x - 1) * (x + 1) - (x - 1) = = (x - 1) * (2x + 2) - (x - 1) = (x - 1) * (2x + 2 - 1) = (x - 1) * (2x + 1)