Численный ответ
(y^3 - x^3)/(3.0*y - 3.0*x)
(y^3 - x^3)/(3.0*y - 3.0*x)
(y^3 - x^3)/(3.0*y - 3.0*x)
(y^3 - x^3)/(3.0*y - 3.0*x)