rubilovalex A-b=(a^1/3)^3-(b^1/3)^3=(a^1/3-b^1/3)*(a^2/3+a^1/3*b^1/3+b^2/3). получаем: a^2/3+a^1/3b^1/3+b^2/3-a^2/3-b^2/3 / (a-b)= a^1/3b^1/3 / (a-b).