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Sin and cos

  1. Mar 14, 2009 #1
    if i have to find the integral of

    sin(n*pi*x/L) * cos(m*pi*x/L) between 0<=x<=L

    is it true that this integral will be 0 every where except where n=m?

    please and thank you.
     
  2. jcsd
  3. Mar 14, 2009 #2
    Is there a trig identity that will simplify this for us a little bit?

    [tex]sin(u)cos(v)=\frac{1}{2}\left[sin(u+v)+sin(u-v)\right][/tex]

    With this trig identity, do you suppose that the integral will be equal to zero when n is not equal to m? When n is equal to m?
     
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