(1)解:(2m-n)^2-(m-2n)^2=4m^2-4mn+n^2-(m^2-4mn+4n^2)=3m^2-3n^2==3(m+n)(m-n)
(2)49(2a-3b)^2-9(a+b)^2=[7(2a-3b)]^2-[3(a+b)]^2=(17a-18b)(11a-24b)
(3)xy(x+y)^2-4x^3y^3=xy(x^2+2xy+y^2-4x^2y^2)==xy[(x+y)^2-4x^2y^2]=xy(x+y-2xy)(x+y-2xy)
(1)解:(2m-n)^2-(m-2n)^2=4m^2-4mn+n^2-(m^2-4mn+4n^2)=3m^2-3n^2==3(m+n)(m-n)
(2)49(2a-3b)^2-9(a+b)^2=[7(2a-3b)]^2-[3(a+b)]^2=(17a-18b)(11a-24b)
(3)xy(x+y)^2-4x^3y^3=xy(x^2+2xy+y^2-4x^2y^2)==xy[(x+y)^2-4x^2y^2]=xy(x+y-2xy)(x+y-2xy)