x-y=1+m y-z=1-m x^2+y^2+z^2-xy-xz-yz=?
问题描述：
x-y=1+m y-z=1-m x^2+y^2+z^2-xy-xz-yz=?
答
x-y=1+m
y-z=1-m
相加
x-z=2
x^2+y^2+z^2-xy-yz-xz
=(2x^2+2y^2+2z^2-2xy-2yz-2xz)/2
=[(x^2-2xy+y^2)+(y^2-2yz+z^2)+(z^2-2xz+x^2)]/2
=[(x-y)^2+(y-z)^2+(z-x)^2]/2
=(1+2m+m^2+1-2m+m^2+4)/2
=3+m^2