Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

From dy/dx to d/dx

  1. Aug 19, 2011 #1
    Hi all,

    This is not strictly a DE question, but I came across this while working on one. This isn't the first time I got this and I just can't remember this from my 1st year maths. Some knowledge would be greatly appreciated. In the answer they do the following:

    [itex](\frac{1}{x})(\frac{dy}{dx}) - (\frac{1}{x^2})y \Rightarrow

    (\frac{d}{dx})[(\frac{1}{x})y][/itex]

    Now I want to know how? I just cant simplify it. Silly question, but need the help!

    Thanks
     
  2. jcsd
  3. Aug 19, 2011 #2

    I like Serena

    User Avatar
    Homework Helper

    Welcome to PF, htdIO! :smile:

    Are you familiar with the chain rule?

    It is: [itex]\frac d {dx} f(y(x)) = \frac {df} {dy} \frac {dy} {dx}[/itex]

    Do you know how to apply this?
     
  4. Aug 19, 2011 #3
    Hi and thanks!

    I do know it. Just not quite sure how I should be applying it here? I've scribbled quite a bit down here now, trying to combine this with the product rule. Or am I heading in the wrong direction?
     
  5. Aug 19, 2011 #4

    I like Serena

    User Avatar
    Homework Helper

    Sorry, you're right. You need to apply the product rule.
    Do you know how to apply it to: [itex](\frac{d}{dx})[(\frac{1}{x})y(x)][/itex]?
     
  6. Aug 19, 2011 #5
    Haha, aah thanks. I must be more tired than I thought...
    I'm guessing the only way to 'see' this (like they did it), is by recognizing it and a bit of practice?
     
  7. Aug 19, 2011 #6

    I like Serena

    User Avatar
    Homework Helper

    Hah, after all the practice I got, I thought you needed the chain rule!
    So much for all that practice! :wink:
     
  8. Aug 19, 2011 #7
    Halfway through I actually remembered the quotient rule, which should make it quicker ;) Anyway, thanks again for getting me on the right track!
     
  9. Aug 19, 2011 #8

    I like Serena

    User Avatar
    Homework Helper

    Neh, the quotient rule is not quicker in this case.
    But good you remembered it! :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: From dy/dx to d/dx
  1. Dx/P = dy/Q = dz/R (Replies: 1)

Loading...