什么意思？
k=-5/6可以么？
f(x y z)=[x^5+y^5+z^5-(5/6)(x^2+y^2+z^2)(x^3+y^3+z^3)]/(x+y+z)
=(x+y+z)[x^3+y^3+z^3-2x^2(y+z)-2y^2(x+z)-2z^2(x+y)+6xyz]/6

感觉在中数上见过...当时扫一眼就放弃了