а+5b a–5b (5b–a)(5b+a)
(----------- – -----------) • ------------------ =
a(a–5b) a(a+5b) 5b^2
(a+5b)^2–(a–5b)^2 –(a–5b)(5b+a)
= --------------------------- • ------------------ =
a(a–5b)(a+5b) 5b^2
–(a+5b–a+5b)(a+5b+a–5b)(a–5b)
= ------------------------------------------------
a(a–5b)(a+5b)•5b^2
(5b+a) –10b•2a 4
--------- = ------------- = – ---
a•5b^2 b