=2a^6+4a^5b+2a^4b^2-5a^5b-10a^4b^2-5a^3b^3-3a^4b^2-6a^3b^3-3a^2b^4+a^2b^3+2a^2b^4+ab^5-4a^2b^4-8ab^5-4b^6=
2a^6-a^5b-11a^4b^2-10a^3b^3-7ab^5-4b^6
=2a^6+4a^5b+2a^4b^2-5a^5b-10a^4b^2-5a^3b^3-3a^4b^2-6a^3b^3-3a^2b^4+a^2b^3+2a^2b^4+ab^5-4a^2b^4-8ab^5-4b^6=
2a^6-a^5b-11a^4b^2-10a^3b^3-7ab^5-4b^6