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Homework Help: Differential notation

  1. Jun 11, 2008 #1
    If one was to differntiate a function implicity eg.

    sin x + cos y = 5,

    would one show this by writing:

    d/dx(sin x + cos y = 5)

    = and then differentiate with respect to x? I wasnt sure whether or not the bracket goes around the whole thing or just the left hand side.


    Thanks
     
  2. jcsd
  3. Jun 11, 2008 #2

    tiny-tim

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    Hi nokia8650! :smile:

    Definitely the whole thing!

    Whatever you do to one side of an equation, you must do to the other.

    :smile: That's what equality is all about! :smile:
     
  4. Jun 11, 2008 #3
    Hmm, I never thought about that. Now I'll know it's correct
    However, I use this notation
    [tex]\sin{x}+\cos{y}=5\mid\cdot{d/dx}[/tex]
    it's just seems more convenient
    That's exactly the same thing isn't it?

    I know it's a REALLY silly question but I just wanted to make sure
     
    Last edited: Jun 11, 2008
  5. Jun 11, 2008 #4

    tiny-tim

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    Hi armis! :smile:

    (are you the same person as nokia8650?)

    I don't really understand that.

    Can you show how the next couple of lines would go, so that we can see it in actual use? :smile:
     
  6. Jun 11, 2008 #5
    Hi tiny-tim

    Nop, I am not the same person :)

    Sure
    [tex]\sin{x}+\cos{y}=5\mid\cdot{d/dx}[/tex]
    We get
    [tex]\cos{x}=0[/tex] if y is not a function of x

    Most of our lecturers do that so I was wondering why bother writting ()
     
  7. Jun 11, 2008 #6

    tiny-tim

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    Hi armis! :smile:

    It looks weird to me …

    but if your lecturers do it, I suppose it's ok.

    I think writing the () is better because it avoids any possibility of ambiguity …

    also, that vertical stroke may be clear on a whiteboard, where the lecturer can make it really large, but it's not so clear on paper or in a book. :frown:
     
  8. Jun 11, 2008 #7
    I find it wierd you haven't seen it :) Well, maby I am the wierd one and it may just be a matter of convenience for the lecturers as sometimes they have to write down REALLY a lot of stuff on the whiteboard
    I am just so used to it that I could hardly think of writting () :)
    But yeah, () avoids any possibility of ambiguity (phew.... that was a hard one for me, I am not an english speaker)
    Indeed the vertical stroke is larger than the one I showed as I couldn't find one large enough in the LaTeX
     
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