# Homework Help: Complex Analysis, Complex Differentiable Question

1. Aug 27, 2013

### BrainHurts

1. The problem statement, all variables and given/known data

Define $f : \mathbb{C} \rightarrow \mathbb{C}$ by

$f(z) = \left \{ \begin{array}{11} |z|^2 \sin (\frac{1}{|z|}), \mbox{when z \ne 0}, \\ 0, \mbox{when z = 0} . \end{array} \right.$

Show that f is complex-differentiable at the origin although the partial derivative $u_x$ is not continous at origin.

2. Relevant equations

3. The attempt at a solution

To show that $f$ is complex differentiable by defintion? In other words

$f'(0)$ = $\lim_{h \rightarrow 0}$ $\frac{f(0+h) - f(0)}{h}$ = $\lim_{h \rightarrow 0} \frac{f(h) - 0}{h}$ = $\lim_{h \rightarrow 0}$ $\frac{|h|^2 \sin(\frac{1}{|h|})}{h}$ = $\lim_{h \rightarrow 0}$ $\frac{h\bar{h} \sin(\frac{1}{|h|})}{h}$ = $0$ ?

Or am I missing something with $\bar{h}$. Because I'm assuming as h approaches 0, so does $\bar{h}$

Also, I see that

$u_x(0,0)$ = $\lim_{x \rightarrow 0}$ $\frac{u(x,0)}{x}$

A little help here, not sure how to approach this problem.

Last edited: Aug 28, 2013
2. Aug 28, 2013

### BruceW

why not write out h in polar form? and see what that implies for $\bar{h}$ as h goes to zero