Ек Екатерина Преобразуем (a^4 – 1) + (2a^3 – 2a) = (a^2 – 1) * (a^2 + 1) + 2a * (a^2 – 1) = (a^2 – 1) * (a^2 + 1 + 2a) = (a – 1) * (a + 1) * (a + 1)^2 = (a – 1) * (a + 1)^3