Rewrite the expression.
(((a+b)/a)-b/(a+b))/(a+b)+(b/a-(a-b)/(a+b))/(a-b)
Point your focus to the fractions in the numerators. Add each set of fractions by multiplying by either a or a+b.
((a+b)^2/(a(a+b))-(b(a+b))/(a(a+b)))/(a+b)+((b(a+b))/(a(a+b))-(a(a-b))/(a(a+b)))/(a-b)
(((a+b)^2-b(a+b))/(a(a+b)))/(a+b)+((b(a+b)-a(a-b))/(a(a+b)))/(a-b)
Simplify the complex fractions by multiplying by 1/(a+b) or 1/(a-b).
(1/(a+b))(((a+b)^2-b(a+b))/(a(a+b)))+(1/(a-b))((b(a+b)-a(a-b))/(a(a+b)))
((a+b)^2-b(a+b))/(a(a+b)^2)+(b(a+b)-a(a-b))/(a(a+b)(a-b))
Simplify.
(a+b-b)/(a(a+b))+(b(a+b)-a(a-b))/(a(a+b)(a-b))
a/(a(a+b))+(b(a+b)-a(a-b))/(a(a+b)(a-b))
Multiply a/(a(a+b)) by (a-b)/(a-b) to combine the fractions.
(a(a-b)-b(a+b)-a(a-b))/(a(a+b)(a-b))
Simplify.
(-b(a+b))/(a(a+b)(a-b))
-b/(a(a-b))