143
(1/b² - 1/a²)* ab/(a+b) = (a²/a²b² - b²/a²b²)* ab/(a+b) = (a²-b²)/a²b² * ab/(a+b) =
(a-b)(a+b)/a²b² * ab/(a+b) = (a-b)/ab.
144
(a/b - b/a) * b/(a-b) = (a²/ab - b²/ab) * b/(a-b) = (a²-b²)/ab * b/(a-b) =
(a-b)(a+b)/ab * b/(a-b) = (a+b)/a.
145
(a²-4)/a * 1/(a+2) - (a+2)/a = (a-2)(a+2)/a * 1/(a+2) - (a+2)/a =
(a-2)/a - (a+2)/a = (a-2-a-2)/a = - 4/a = - ⁴/ₐ.