∵ y+z?x x+y?z = z+x?y y+z?x = x+y?z z+x?y =k，∴k3= y+z?x x+y?z ? z+x?y y+z?x ? x+y?z z+x?y =1，∴k=1，k2=1，则k1+k2+k3=1+1+1=3．
