### Author Topic: Q10 in Section 1.3  (Read 335 times)

#### Jing Yang

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##### Q10 in Section 1.3
« on: September 30, 2020, 11:48:24 AM »
Is there anyone who knows how to figure out this question? I used the polar representation of z that is $z=|z|e^{i\theta}$, and do the square of z. Is this step correct and what next? Thanks!

#### RunboZhang

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##### Re: Q10 in Section 1.3
« Reply #1 on: September 30, 2020, 09:30:19 PM »
I think we have restricted arg(z) to (pi/2,pi). After expanding z^2 = (e^i*theta)^2, you will observe that the argument changes to (pi,2pi), which indicates that the second quadrant (excluding axis) is getting mapped to the lower half of the complex plane (still excluding the axises). Thus you can easily prove that this set is open and connected. That is what I think about this question, correct me if I am wrong.