✔ 最佳答案
x^3+y^3+z^3=3xyz為什麼會x=y=z
Sol
x^3+y^3+z^3=3xyz
x^3+y^3+z^3-3xyz=0
(x+y+z)(x^2+y^2+z^2-xy-yz-xz)=0
x+y+z=0 or x^2+y^2+z^2-xy-yz-xz=0
考慮 x^2+y^2+z^2-xy-yz-xz=0
2x^2+2y^2+2z^2-2xy-2yz-2xz=0
(x^2-2xy+y^2)+(y^2-2yz+z^2)+(x^2-2xz+z^2)=0
(x-y)^2+(y-z)^2+(x-z)^2=0
x=y=z
再考慮 x+y+z=0時
x=1,y=2,z=-3
x^3+y^3+z^3-3xyz
=1^3+2^3+(-3)^3-3*1*2*(-3)
=0
So
x^3+y^3+z^3=3xyz無法導出x=y=z
但
x^3+y^3+z^3=3xyz,x+y+z<>0=>x=y=z