a3-b3=a3-a2b+a2b-b3=a2(a-b)+b(a2-b2)=a2(a-b)+b(a+b)(a-b)
=(a2+ab+b2)(a-b)
a3+b3=a3+a2b-a2b+b3=a2(a+b)-b(a2-b2)=a2(a+b)-b(a+b)(a-b)
=(a2-ab+b2)(a+b)