A^2-3ab 7ab-25b^2 a^2-3ab 7ab-25b^2 a^2-3ab-7ab-25b^2
----------- - --------------- = ------------ + -------------- = -------------------------- =
(a-5b)^2 (5b-a)^2 (a-5b)^2 (a-5b)^2 (a-5b)^2
a^2-10ab-25b^2 (a-5b)^2
= --------------------- = ------------ = 1
(a-5b)^2 (a-5b)^2