已知,xyz=0,求x/(xy+x+1)+y/(yz+y+1)+z/(xz+z+1）值?

同学,xyz=1吧?
这样的话,
原式=x/(xy+x+xyz)＋y/(yz+y+xyz)＋z/(xz+z+xyz)
=1/(y+1+yz)+1/(z+1+xz)+1/(x+1+xy)
=xyz/(y+xyz+yz)+1/(z+1+xz)+1/(x+1+xy)
=xz/(1+xz+z)+1/(z+1+xz)+1/(x+1+xy)
=(xz+1)/(z+1+xz)+1/(x+1+xy)
=(xz+xyz)/(z+xyz+xz)+1/(x+1+xy)
=(x+xy)/(1+xy+x)+1/(x+1+xy)
=1

xyz=0?