|xy+z1yx+z1zx+y1=
xyz
z+y+z
0
x2+y2+z2
|xy+z1yx+z1zx+y1=|x+y+zy+z1x+y+zx+z1x+y+zx+y1 (c1→c1+c2) =x+y+z|1y+z11x+z11x+y1=0