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Summation for y(x)=Absolute value(sin(x)) -pi<x<pi

  1. Oct 16, 2013 #1
    i want to use the fourier method to fins an summation for
    y(x)=Absolute value(sin(x)) -pi<x<pi

    i know that cos(pi*n)=(-1)^n

    and get why they use cos(pi*(n+1))= (-1)^(n+1)

    but why is then cos(pi*(n-1)) also (-1)^(n+1)


    (see attachment)

    THANX!!
     

    Attached Files:

  2. jcsd
  3. Oct 16, 2013 #2

    jedishrfu

    Staff: Mentor

    look at the two expressions:

    (-1)^(n+1) ==> (-1)^n * (-1)

    and

    (-1)^(n-1) ==> (-1)^n*(1/(-1)) = (-1)^n * (-1)

    so they are interchangeable.
     
  4. Oct 16, 2013 #3
    Thank you!!
     
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