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Homework Help: Derivative of: y=arctan(4/x)

  1. Jul 30, 2008 #1
    derivative of: y=arctan(4/x)!!!

    This seems like it should be a very SIMPLE problem, but it has been bugging me for about 2 hours straight now, and I can't figure it out! Would really appreciate some quick help...

    This is what I've done so far:

    y'= -4/x^2 / (16/x^2 +1)

    I dont know if this is the right answer??? And I am having problems simplifying this any further. Please help :P
     
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  3. Jul 30, 2008 #2

    Dick

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    Re: derivative of: y=arctan(4/x)!!!

    That's fine. Now use algebra. (a/b)/c=a/(b*c).
     
  4. Jul 30, 2008 #3

    rock.freak667

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    Re: derivative of: y=arctan(4/x)!!!

    Yes that is correct.But you can simply further by multiply both the numerator and denominator by x^2

    EDIT: ahh beaten
     
  5. Jul 30, 2008 #4

    Dick

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    Re: derivative of: y=arctan(4/x)!!!

    It's not a race. Good advice is best given in large quantities. I made that aphorism up just now. :)
     
  6. Jul 30, 2008 #5
    Re: derivative of: y=arctan(4/x)!!!

    Ok great thanks,

    Now for this next part, I guess the thing that is throwing me off is the +1 hanging off the denominator.

    So, following these steps, I would come out with:

    -4/16 + x^2

    ...

    which I could then reduce further to:

    -1/4+x^2

    Would that make sense?
     
  7. Jul 30, 2008 #6

    Dick

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    Re: derivative of: y=arctan(4/x)!!!

    You should really review some algebra. Yes, to -4/(16+x^2). A big thumbs down to -1/4+x^2. They aren't at all the same, are they? And use more parentheses to group terms, ok?
     
  8. Jul 30, 2008 #7
    Re: derivative of: y=arctan(4/x)!!!

    Yah, I think I do need some algebra review. That was a really simple error I just made, and this problem took me WAY too long to figure out.

    Thanks alot for the quick responses...I just signed up for these forums, and hoped that I would be able to get a respone within the hour, but you sure beat that!

    Regarding the question, -4/(16+x^2) has been reduced, and I will leave it like this, which I think is the correct answer. So thanks again guys!
     
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