9(a-b)^2-25(a+b)^2
=[3(a-b)]^2-[5(a+b)]^2
=(3a-3b)^2-(5a+5b)^2
=[(3a-3b)+(5a+5b)][(3a-3b)-(5a+5b)]
=(3a-3b+5a+5b)(3a-3b-5a-5b)
=(8a+2b)(-2a-8b)
=-(8a+2b)(2a+8b)
=-4(4a+b)(a+4b)
看完了采纳哦~~祝学习进步!