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Help understanding question

  1. Apr 5, 2004 #1
    The question asks to prove the following by writing each sine and cosine function as a sum of exponentials of arguments inwt or imwt:

    integral from -pi/w to pi/w (cos (nwt)cos(mwt) dt) = {0 for n not equal to m, pi/w for n=m not equal to 0 , 2pi/w for n=m=0

    Would I write the cosine funtion in the exponential form e^x+e^-x/2 and then solve by using different valuse for n and w for the one the is equal to 0 when n is not equal to m? I'm confused.
  2. jcsd
  3. Apr 5, 2004 #2


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    Split the job in two cases
    1. You are to show that the integral is zero whenever n is not m.
    2. You are to show that the integral is the value indicated whenever n=m
    If you are unfamiliar with the exponential form, you might use:
  4. Apr 6, 2004 #3

    I still don't get it. Can someone show me an example? Do i have to chose two different numbers for n and m?
  5. Apr 7, 2004 #4

    matt grime

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    You must do it for general n and m. Specifying them for a couple of values does not prove the result for all n and m. Just leave the n and m in there as letters (constants) and do the integration.
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