a+b+c=0,证明a^3+b^3+c^3=3abc
问题描述:
a+b+c=0,证明a^3+b^3+c^3=3abc
答
c= -(a+b)
a^3+b^3+c^3
=a^3+b^3-(a+b)^3
=a^3+b^3-(a^3+3a^2b+3ab^2+b^3)
= -(3a^2b+3ab^2)
= -3ab(a+b)
=3abc