Cosine question

  • Thread starter Moneer81
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  • #1
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Homework Statement


While solving the integral of a wave function,I came across the term cos(n*pi) , where n is an integer. Is that term equal to +1 or -1 (I know that it could be either one depending on whether n is odd or even) but how do I proceed with the integral?


Homework Equations



none

The Attempt at a Solution



cos (n*pi) is 1 if n is even and -1 if n is odd...but how do proceed?

thanks a lot
 

Answers and Replies

  • #2
Tom Mattson
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Why does n have to be +1 or -1? Why can't it be 2, for instance?
 
  • #3
159
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n could be any integer, but the whole term cos (n*pi) will have to be +1 or -1
 
  • #4
Tom Mattson
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OK, so you're trying to integrate and you have somewhere a factor of [itex]\cos(n\pi)[/itex], where [itex]n[/itex] is an integer. Is that right? In that case you can just replace [itex]\cos(n\pi)[/itex] with [itex]\pm 1[/itex].

This looks pretty straightforward to me. It might help me understand why this is giving you trouble if you typed out the integral that you are trying to do, what you have done, and where you got stuck.
 
  • #5
141
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You can write the term as

[tex]
\cos(n\pi) = (-1)^{n}
[/tex]

It doesn't really help that much, but you see this a lot. Since this is a constant term you can just proceed to perform the integral you want to evaluate.
 

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