a^7-(ab)^6
=a^6(a-b^6)...............................................................................................................................................................................................................................................坑爹啊.....難道不是？不好意思說錯了看補充對不起！?。^7-ab^6=a(a^6-b^6)=a(a^3-b^3)(a^3+b^3)=a(a-b)(a+b)(a^2+ab+b^2)(a^2-ab+b^2)就是公式a^3-b^3=（a-b)(a^2+ab+b^2)a^3+b^3=(a+b)(a^2-ab+b^2) ab(c^2-d^2)-(a^2-b^2)cd=abc^2-abd^2-a^2cd+b^2cd=ac(bc-ad)+bd(bc-ad)=(ac+bd)(bc-ad)