m^7+m^4n^3-m^3n^4-n^7
=m^4(m^3+n^3)-n^4(m^3+n^3)
=(m^3+n^3)(m^4-n^4)
=(m^3+n^3)(m^2-n^2)(m^2+n^2)
=(m^3+n^3)(m+n)(m-n)(m^2+n^2)