令u=x-y, v=y-z则F(u,v)=0两边对x求偏导:∂F/∂u*∂u/∂x+∂F/∂v*∂v/∂x=0即∂F/∂u+∂F/∂v*(-∂z/∂x)=0, 得:∂z/∂x=(∂F/∂u)/(∂F/∂v)=F'u/F'v两边对y求偏导:∂F/∂u*∂u/∂y+∂F/∂v*∂v/∂y=0即∂F/∂u*(-1)+∂F/∂v(1-∂z/∂y)=0,得:∂z/∂y=(F'v-F'u)/F'v因此有∂z/∂x+∂z/∂y=(F'u+F'v-F'u)/F'v=F'v/F'v=1