(m+n)^3+2m(m+n)^2+m^2(m+n)
=(m+n)((m+n)^2+2m(m+n)+m^2)
=(m+n)(m+n+m)^2
=(m+n)(2m+n)^2
(a^2+b^2)^2-4a^2b^2
=(a^2+b^2+2ab)(a^2+b^2-2ab)
=(a+b)^2(a-b)^2
(m+n)^3+2m(m+n)^2+m^2(m+n)
=(m+n)((m+n)^2+2m(m+n)+m^2)
=(m+n)(m+n+m)^2
=(m+n)(2m+n)^2
(a^2+b^2)^2-4a^2b^2
=(a^2+b^2+2ab)(a^2+b^2-2ab)
=(a+b)^2(a-b)^2