x-3=y-2=z-1
得x-y=1,y-z=1,z-x=-2,x-z=2
x得平方+y的平方+z的平方-XY-YZ-ZX
=x*(x-y)+y*(y-z)+z*(z-x)
=x*1+y*1+z*(-2)
=x+y-2z
=(x-z)+(y-z)
=2+1=3