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Homework Help: Fourier series pleeeease

  1. May 21, 2008 #1
    fourier series pleeeease :(

    Hi every one,

    I want your help please. I have a difficulty in answering these questions.

    Actually it seems simple but I could not answer them because I did not understand the lesson very well.

    This homework worths 5% and I have to hand it as soon as possible!

    Find the fourier series expansion for the function over the specified intervals:-

    1- f(x)= 1, -∏< x < ∏

    2- f(x)= 0, -∏< x < 0 and x^2, 0< x < ∏

    Find fourier cosine series:-

    - f(x)= x, 0< x < ∏

    Find fourier sine series:-

    - f(x)= -x, 0< x < 1
  2. jcsd
  3. May 21, 2008 #2


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    Science Advisor
    Homework Helper

    yes, but you have to show attempt to solution and what relations you know of dude. Otherwise you can't get help. It is agaist the forum rules.

    If you do this, write the relations you know of, and at least a start from your side. Then I'll kick you in the right direction.
  4. May 21, 2008 #3
    Thank you for telling me.

    Actually I started by finding a(0) and a(n) and b(n)

    my attempt for the first question
    a(0)= 2 (final answer)

    a(n)= I think 0

    b(n)= ((-1)^n-(-1)^n)/(n) which is I am really not sure about

    And if I get these three answers, should I only substitute it in the main equation OR I have to go in further steps?!

    Thank you again my dear
  5. May 22, 2008 #4


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    Homework Helper

    How did you get 2?

    To find a(n) and b(n), note that f(x) is an even function. So what does that tell you about a(n) and b(n)?

    Once you get a(n) and b(n) just substitute them into the expression for the Fourier series.
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