Question 321263
1/a-b - 3ab/a^3-b^3
LCM = a^3-b^3
..
a^2+ab+b^2-3ab / a^3-b^3
a^2-2ab+b^2 / a^3-b^3
(a-b)^2 / (a-b)(a^2+ab+b^2)
(a-b) / (a^2+ab+b^2)