x-y=(1+√3)/2 .....(1)z-y=(1-√3)/2 ......(2)(1)-(2)：(x-z)=√3 .....（3）(1)²+(2)²+(3)²得：(x-y)²+(z-y)²+(x-z)² = [(1+√3)/2]²+[(1-√3)/2)]²+[√3]²2x²+2y²+2z²-2xy-2yz-2xz = 5x²+y²+z²-xy-yz-xz = 5/2
