(6x - 18x^2) / (y - 3x)^3 = -6x + 18x^2 / -(3x - y)^3 = -6x + 18x^2 / -27x^3 + 27x^2y - 9xy^2 + y^3 = -2 / 9x - 2y + 6y^2 / 27x^2 - 27xy + 9y^2 - y^3
(6x - 18x^2) / (y - 3x)^3 = -6x + 18x^2 / -(3x - y)^3 = -6x + 18x^2 / -27x^3 + 27x^2y - 9xy^2 + y^3 = -2 / 9x - 2y + 6y^2 / 27x^2 - 27xy + 9y^2 - y^3