答：
x=2,x+y+z=-2.8
2+y+z=-2.8
y+z=-4.8
x²(-y-z)-3.2x(z+y)
=-x(y+z)(x+3.2)
=-2×(-4.8)×(2+3.2)
=9.6×5.4
=51.84答案正确吗0w0sorry，应该是5.2不是5.4：x²(-y-z)-3.2x(z+y)=-x(y+z)(x+3.2)=-2×(-4.8)×(2+3.2)=9.6×5.2=49.92啊咧Σ(ﾟдﾟ；)真有错的啊sorry，敲字敲错了~~