Power Expansion (Complex variables)

  • Thread starter tmlfan_17
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  • #1
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Homework Statement



Use the power series for e^z and the def. of sin(z) to check that
sum ((-1)^k z^(2 k+1))/((2 k+1)!)

Homework Equations





The Attempt at a Solution



I apologize, but I am not particularly good with latex. Therefore, I attached a picture of my solution thus far. I've tried many methods, but this is where I get stuck and I can't seem to get sin(z) to equal its power expansion. Any help would be very much appreciated.
 

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Answers and Replies

  • #2
3,816
92
So you have:
$$\frac{1}{2i}\sum_{n=0}^{\infty} \frac{z^n}{n!}\left(i^n-(-i)^n\right)$$
Clearly, if ##n## is even, ##i^n-(-i)^n=0##. Can you figure out what happens if ##n## is odd i.e ##n## is of the form ##2k+1##?
 
  • #3
11
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Yes. Thank you sir!
 
  • #4
3,816
92
Yes. Thank you sir!

Glad to help but please don't call me sir, I am a student myself. :smile:
 

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