题目是否错了应该改为(x+y+z)^2-4(x-y-z)^2
(x+y+z)^2-4(x-y-z)^2=[(x+y+z)-2(x-y-z)][(x+y+z)+2(x-y-z)]
=(3Y+3Z-X)(3X-Y-Z)