3x^2+12xy=3x(x+4y)
ad-ac+7d-7c=a(d-c)+7(d-c)=(d-c)(a+7)
25a^2-(a-3)^2=(5a)^2-(a-3)^2=(5a-(a-3))(5a+(a-3))=
=(5a-a+3)(5a+a-3)=(4a+3)(6a-3)=(4a+3)*3(2a-1)=3(4a+3)(2a-1)
3x^2+12xy=3x(x+4y)
ad-ac+7d-7c=a(d-c)+7(d-c)=(d-c)(a+7)
25a^2-(a-3)^2=(5a)^2-(a-3)^2=(5a-(a-3))(5a+(a-3))=
=(5a-a+3)(5a+a-3)=(4a+3)(6a-3)=(4a+3)*3(2a-1)=3(4a+3)(2a-1)