Calculate the Fourier Sine Series of f(x)=sin(x/2)

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Discussion Overview

The discussion revolves around calculating the Fourier Sine series for the function f(x) = sin(x/2) over the interval (0, π). Participants explore various approaches to derive the series and clarify the periodicity of the function.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant requests assistance in finding the Fourier Sine series for f(x) = sin(x/2) over the specified interval.
  • Another participant asserts that sin(x/2) is already a periodic function with period π, suggesting that the Fourier series would yield the same function.
  • A different participant proposes using the standard Fourier series for sin(X) and substituting X with x/2 as a method to find the series.
  • There is a contention regarding the periodicity of sin(x/2), with one participant questioning whether it has a period of 4π instead of π.
  • One participant mentions difficulties in calculating the coefficients a_n, noting that b_n is zero while a_n is not, and seeks clarification on a related cosine equality.
  • Another participant challenges the validity of the cosine equality presented, providing reasoning for why it cannot hold true.
  • A participant acknowledges a realization regarding the integration in series, suggesting a correction to their earlier statement about the cosine equality.
  • One participant suggests using the regular Taylor series instead of Fourier series, but another counters that the exam specifically requires the Fourier approach.
  • There is an acknowledgment that the answers would differ between the Fourier and Taylor series methods.

Areas of Agreement / Disagreement

Participants express differing views on the periodicity of sin(x/2) and the validity of certain mathematical statements. There is no consensus on the correct approach to finding the Fourier Sine series, and the discussion remains unresolved.

Contextual Notes

Participants reference specific mathematical properties and series expansions, but there are unresolved assumptions regarding the periodicity and the calculations of coefficients. The discussion also highlights the context of an exam requirement for using Fourier series specifically.

nizama
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Hi there!

Can anyone please help me with this one..?

Find the Fourier Sine series of f(x)=sin(x/2) for interval (0,pi)

thanx a lot :)
 
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well, sin(x/2) is already a periodical function with period pi, so even if you construct a furier series of this one you would get the same: sin(x/2)
 
get the standard Fourier series for sin(X) and replace X=x/2, and that's it!
 
well, sin(x/2) is already a periodical function with period pi

Wouldn't it have a period of 4pi?
 
Well hmm...not really :rolleyes:

I did get almoust correct answer BUT...
you see b_n is zero but a_n is not...and this is where i stuck ...i can't get correct a_n
by the way...can you tell me is this true?

cos(npi) + cos(0pi) = (-1)^(n+1)

thanx again :smile:
 
(Assuming n is an integer). It's not true. cos(npi) is either 1 or -1, and cos(0pi) = cos(0) = 1, so the LHS is either 1 + 1 = 2 or -1 + 1 = 0, while the RHS is either 1 or -1... So you can never get equality.
 
aha

Yes i just got it..
it is when you use integr. in series
so then it would be ((-1)^n +1)

thanx

:smile:
 
couldn't you just use the regular Taylor series?
 
hm

Not really :frown:
the task...as so on my exam..they strictly want it with Fourier ...
bcs we do also taylor..and in task they mention which one they want..
 
  • #10
THe answers would be different for a start as well.
 

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