1、(a+b)^3=a^3+b^3+3a^2b+3ab^2=a^3+b^3+3ab(a+b)
已知(a+b)=1
所以a^3+b^3+3ab=a^3+b^3+3ab(a+b)=(a+b)^3=1
2、(a+b+c)^3
=a^3+b^3+c^3+3a^2b+3ab^2+3a^2c+3ac^2+3b^2c+3bc^2+6abc
=a^3+b^3+c^3+3ab(a+b)+3ac(a+c)+3bc(b+c)+6abc
=a^3+b^3+c^3+3ab(a+b+c)-3abc+3ac(a+b+c)-3abc+3bc(a+b+c)-3abc+6abc
=a^3+b^3+c^3+3ab(a+b+c)+3ac(a+b+c)+3bc(a+b+c)-3abc
a^3+b^3+c^3=(a+b+c)^3-[3ab(a+b+c)+3ac(a+b+c)+3bc(a+b+c)-3abc]
已知a+b+c=0
所以a^3+b^3+c^3=3abc
同理x^3+y^3+z^3=3xyz
所以a^3+b^3+c^3/x^3+y^3+z^3=3abc/3xyz=abc/xyz