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### Topics - hanyu Qi

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##### MAT334--Lectures & Home Assignments / FE Sample Question 4 (a)
« on: December 07, 2018, 05:28:43 PM »
Hello, I am wondering whether we can have different function f(z) for this question.

In the posted solution, Yilin set $f(z) = \lambda \frac{z-a}{1-\bar{a}z}$ $| \lambda | = 1$ and get final result as $f(z) = \frac{5+z}{1+5z}$.

Based on a hint in Textbook 3.3 Example 1, I try to set $f(z) = \lambda \frac{a-z}{1-\bar{a}z}$ and $| \lambda |=1$then I did the following computation.

let $\lambda = e^{it}$ , $a = re^{i \theta}$

$f(0) = 5$ -> $\lambda a = 5$ and $|\lambda a| = |a| = 5$ so $a = 5e^{i\theta}$

$\lambda a = 5e^{it} e^{i\theta} =5$ so $e^{-it} = e^{i\theta}$

$f(-1) = \lambda \frac{a+1}{1+\bar{a}} = -1$ so $e^{-i\theta} = -1$ ---> $e^{it} =1$ and $\theta = \pi$

so $\lambda = 1$ and $a = -5$

$f(z) = \frac{-5-z}{1-5z}$

I am not sure if there is a computation mistake for my solution or we could set f(z) in many forms.

Thank you.

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##### MAT334--Lectures & Home Assignments / TT2 Q4 Question for step4
« on: December 02, 2018, 01:36:30 PM »
Hello everyone, I am wondering why the range of $\theta$ is $[0,\pi]$ instead of $[\pi,0]$.

Then the integral estimation would be $|\int_{\gamma_{\epsilon}} f(z) \text{d}z| \leq \int_{\pi}^{0} |f(z)| \text{d}z = \frac{-\pi \epsilon}{\sqrt{\epsilon} (1-{\epsilon}^2)}$ goes to 0 as $\epsilon$ close to 0+.

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##### MAT334--Lectures & Home Assignments / Section 2.1 Question 1
« on: October 15, 2018, 04:50:02 PM »
Hello everyone,

I am wondering whether I need to show a function is differentible first then calculate the derivative even if the question only ask me to establish the derivative.

E.X.  (sinZ)’ = cosZ

The answer uses the limit definition to show but can I use theorem 3 (C-R equations) to show it as well?

Thank you!

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