25a2 − 9 is factored as

(5a + 3)(5a − 3) (5a + 1)(5a − 9) (5a − 3)2 (25a + 1)(a − 9)

(5a + 3)(5a − 3)

We know, (a2 – b2) = (a – b)(a + b) Given = 25a2 – 9 = (5a)2 – 32                                                     = (5a – 3) (5a + 3)