= (3a+b)/(ab(a-b)) - (a-b)/ab * (3a-b)/((a-b)(a+b)) = (3a+b)/(ab(a-b)) - (3a-b)/(ab(a+b)) = (3a²+3ab+ab+b²-3a²+ab+3ab-b²)/(ab(a-b)(a+b)) = 8ab/(ab(a-b)(a+b)) = 8/(a²-b²)
