25(3a+2b)^2 -4(3a-2b)^2
=[5(3a+2b]² - [2(3a-2b)]²
=[5(3a+2b) +2(3a-2b)]*[5(3a+2b) -2(3a-2b)]
=(21a-6b)(9a+14b)
=3(7a-2b)(9a+14b)