(a+b)^3=a^3+b^3+3a^2b+3ab^2(a-b)立方？（a-b）立方=a^3-b^3-3ab（a-b）=a^3-b^3-3a^2b+3ab^2a^3-b^3=?谢谢(a^3-b^3)=(a-b)(a^2+ab+b^2)