(1)=a^2b(b^2-4)=a^2b(a+2)(a-2)
(2)=(a+b)(a-b)+(a+b)=(a+b)(a-b+1)
(3)=x^2(x+y)-y^2(x+y)=(x^2-y^2)(x+y)=(x+y)^2(x-y)