Fourier Series (Half-range expansion)

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SUMMARY

The discussion centers on the concept of Fourier Series, specifically focusing on half-range expansions. A key point is the importance of correctly identifying the length of the interval (L), which should be π for half-range expansions. Participants clarify that using L as π ensures all basis functions are utilized, avoiding the omission of half the interval. The confusion arises from the difference between the teacher's solution, which uses "sin nx," and the student's "sin 2nx," highlighting the significance of understanding the basis functions in relation to the specified interval.

PREREQUISITES
  • Understanding of Fourier Series and their applications
  • Knowledge of half-range expansions in Fourier analysis
  • Familiarity with trigonometric functions and their properties
  • Basic calculus concepts related to integration and series
NEXT STEPS
  • Study the derivation of Fourier Series for different intervals
  • Learn about the implications of half-range expansions on function representation
  • Explore the relationship between interval length and basis functions in Fourier analysis
  • Investigate common mistakes in Fourier Series calculations and how to avoid them
USEFUL FOR

Students studying mathematical analysis, particularly those focusing on Fourier Series, as well as educators seeking to clarify concepts related to half-range expansions.

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Homework Statement



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Homework Equations



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The Attempt at a Solution



I don't really understand why my solution is wrong as I think I have substituted everything in correctly..

Is it okay if anyone can help me take a look at my solution? Thank you. :)

My solution: (Only bn)

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My teacher's solution (not the whole solution):

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The thing I don't understand is why is my teacher's sin portion "sin nx" and not "sin 2nx" like mine?

Thanks. :)
 
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Your L should be pi. As it is now you are missing half of the interval and not using all of the basis functions.
 
Orodruin said:
Your L should be pi. As it is now you are missing half of the interval and not using all of the basis functions.

I see. Is this due to the half-range expansion, or is it because of the range from (0, π)?

Thank you. :)
 
Well, both. The half-range is 0 to pi so the length of the full range must be 2pi. In the end, you could just as well have considered it to be just an expansion on 0 to pi without making an extension, the basis functions are the same.
 
Orodruin said:
Your L should be pi. As it is now you are missing half of the interval and not using all of the basis functions.

I see. Just wondering, if this is just a normal Fourier series expansion of cos(x) from (0,π), will the L still be the same?
 

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