沒(méi)有陽(yáng)光的動(dòng)人：
∵3(x²+y²+z²)=(x+y+z)²
即3x²+3y²+3z²=x²+y²+z²+2xy+2yz+2xz
2x²+2y²+2z²=2xy+2yz+2xz
2x²+2y²+2z²-2xy-2yz-2xz=0
(x²+y²-2xy)+(y²+z²-2yz)+(x²+z²-2xz)=0
(x-y)²+(y-z)²+(x-z)²=0
且(x-y)²≥0,(y-z)²≥0,(x-z)²≥0
∴x-y=0,y-z=0,x-z=0
解得x=y=z
∴x、y、z的關(guān)系是相等的