b)
(a+b)^3+(a-b)^3
=(a+b+a-b)((a+b)^2-(a+b)(a-b)+(a-b)^2)
=2a(a^2+2ab+b^2-a^2+b^2+a^2-2ab+b^2)
=2a(3b^2+a^2)
c) (a+b)^3-(a-b)^3
=(a+b-(a-b))((a+b)^2+(a+b)(a-b)+(a-b)^2)
=2b(a^2+2ab+b^2+a^2-b^2+a^2-2ab+b^2)
=2b(3a^2+b^2)
còn câu a anh thấy sao sao ây. chắc có lẻ trình độ của anh thấp







