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How to re-write this expression?

  1. Mar 12, 2013 #1
    Could someone please help me make this expression a little smaller? I'm sure there are things that cancels out or could be re written, but I generally suck at these things as I tend to break a few math rules along the way.
    Could I for instance cancel n against n in the two last cosine expressions so I'm left with -cos∏-cos∏/2 at the end?

    Expression is here: http://tinypic.com/r/2lw8047/6
     
  2. jcsd
  3. Mar 12, 2013 #2

    Ray Vickson

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    Absolutely NOT! ##\cos(n \pi)/n## is most definitely not equal to ##\cos(\pi).## Just evaluate ##\cos(n \pi)/n## for ##n = 2, 3, 4## and see what you get.

    Vital advice: put out of you mind forever any thought that you can cancel n's in such situations. Never try to cancel the n's in expressions like ##\cos(nx)/n, \; \sin(nx)/n, \: e^{nx}/n, \; \log(nx)/n, ## etc. You just cannot do it.
     
  4. Mar 12, 2013 #3

    LCKurtz

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    To add to what Ray said, you can give expressions for ##\cos (n\pi)## and ##\cos(\frac{n\pi} 2)## that don't involve cosines. Write them out for a few values of ##n## to see a pattern.
     
  5. Mar 12, 2013 #4

    SteamKing

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    You must learn to think of sin, cos, etc. as functions.

    If y(x) were defined as some function, I don't think you would say that

    y(5n)/n was the same as y(5).
     
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