u/？ x=2x，？ u/？ y=0

v/？ x=0，？ v/？ y=2y

According to Cauchy Riemann equation:

u/？ x=？ v/？ y→2x=2y→x=y

u/？ y=-？ v/？ X is established

So f(z) is differentiable on the straight line y = x.

But f(z) is not differentiable at any point outside the straight line,

The analysis of f(z) at a certain point requires that it can be differentiated in a neighborhood of that point, so f(z) is not analyzed anywhere in the z plane.