Factorize each of the following expression:

$49(a-b)^{2}-25(a+b)^{2}$

$=[7(a-b)]^{2}-[5(a+b)]^{2}$

$=[7(a-b)-5(a+b)][7(a-b)+5(a+b)]$

$=(7 a-7 b-5 a-5 b)(7 a-7 b+5 a+5 b)$

$=(2 a-12 b)(12 a-2 b)$

$=2(a-6 b) 2(6 a-b)$

$=4(a-6 b)(6 a-b)$