(x+y+z)²+(x-y-z)(x-y+z)-2·z(x+y)=(x+y)²+2z(x+y)+z²+(x-y)²-z²-2z(x+y)=(x+y)²+(x-y)²=(x-y)²+4xy+6²=6²-4x8+36=72-32=40如果本题有什么不明白可以追问,...