I'm looking at a problem involving complex numbers and a proof. It shows the solution too, but I don't get how they did a certain step.(adsbygoogle = window.adsbygoogle || []).push({});

At one step they end up with this: (NOTE: the sigma should have 'n=0' on bottom and infinity on top, but I don't know how to do that in latex. If someone knows, please share):

[tex]Im(e^{i\theta}\sum(re^{2i\theta})^{n})[/tex]

Then in the next step they get from the above to the below:

[tex]Im(e^{i\theta}\frac{1}{1-re^{2i\theta}})[/tex]

If someone could please explain how they are equal I would greatly appreciate it.

I didn't include the default template for threads on this section of the forum because I don't think it really applies to this question, if I'm wrong then I appologize. I didn't really attempt much of a solution, other than just writing out the sums to see if I could do anything with that... no luck.

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# Complex number

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