a^3+b^3=(a+b)*(a^2-ab+b^2)
a^3-b^3=(a-b)*(a^2-ab+b^2)
(a+b）^3=a^3+3(a^2)b+3(b^2)a+b^3
(a-b）^3=a^3-3(a^2)b+3(b^2)a-b^3等学习二项式定理后,你就明白了