令x=0,则
(x+y+z)^5-(x+y-z)^5-(x-y+z)^5-(-x+y+z)^5
=(y+z)^5-(y-z)^5-(-y+z)^5-(y+z)^5
=0
所以分解式中含因式x,同理可得也含y、z
从而分解式中含因式xyz
又因为(x+y+z)^5-(x+y-z)^5-(x-y+z)^5-(-x+y+z)^5是五次轮换对称式,
所以除去xyz外,还有二次轮换对称式,
只能是k(x^2+y^2+z^2)
或者k[(x+y)^2+(y+z)^2+(z+x)^2]
或者k[(x-y)^2+(y-z)^2+(z-x)^2
用代定系数法可算出k=80,并排除后两种情况,
可得,原式=80xyz(x^2+y^2+z^2)