若x-y+z=-4,x^2-(y+z)^2=8,则x+y+z=
问题描述：
若x-y+z=-4,x^2-(y+z)^2=8,则x+y+z=
如题
答
x-(y+z)=-4
x²-(y+z)²=8
[x+(y+z)][x-(y+z)]=8 /平方差公式
(x+y+z)[x-(y+z)]=8
x+y+z=8/[x-(y+z)]=8/(-4)=-2