（x-y+z）²-(x+y-z)²

　　=[(x-y+z)+(x+y-z)][(x-y+z)-(x+y-z)]

　　=(x-y+z+x+y-z)(x-y+z-x-y+z)

　　=2x×(-2y+2z)

　　=-4xy+4xz

　　=-4x(y-z)