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Integral of trigonometric functions

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data

    How can I integrate this:

    [tex]\int sin (nt) sin (n \pi t) dt [/tex]

    This actually in the Fourier series.
     
  2. jcsd
  3. Dec 1, 2009 #2

    LCKurtz

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    Use the trig identity:

    [tex] \sin\theta\sin\phi=\frac{\cos{(\theta-\phi)}-\cos{(\theta+\phi)}}{2}[/tex]
     
  4. Dec 1, 2009 #3
    You can use the following identity:

    [tex]\sin a \sin b=\frac{\cos(a-b)-\cos(a+b)} 2[/tex]
     
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