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C3 Differentation - TAKES TWO SECS watch

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    My notes are 'patchy' at best...

    Could someone tell me if this is correct please.

    y = 3/x dy/dx = 3lnx

    y= 1/3x dy/dx = ln3x
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    No, you've integrated.

    y=3/x means y = 3x-1
    Differentiate that and you get dy/dx = -3x-2

    Well, you've integrated for the first one. You've done something very weird for the second one! :s:
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    no....if y=3lnx....dy/dx will be 3/x

    if y=ln3x dy/dx=1/3x....you've got it the wrong way round!
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    (Original post by christina.s)
    no....if y=3lnx....dy/dx will be 3/x

    if y=ln3x dy/dx=1/3x....you've got it the wrong way round!
    If Y = ln3x , I thought dy/dx = 1/x

    as ln3x can be ln3+lnx..

    ln3 is just a number

    so you just differentiate lnx = 1/x
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    Balls.

    Thanks for that. Is what i posted originally correct in terms of integration?
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    (Original post by Jimi Haze)
    If Y = ln3x , I thought dy/dx = 1/x

    as ln3x can be ln3+lnx..

    ln3 is just a number

    so you just differentiate lnx = 1/x

    yeh....you're right!!!i really shouldnt be taking my c3exam on thursday!
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    You've got problems? Mine's tomorrow morning.
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    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
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    Indeed, d(ln3x)/d(x)=1/x, because differentiating ln (f(x)) gives f'(x)/f(x). If f(x)=3x, f'(x)=3, so dy/dx = 3/3x=1/x.
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    (Original post by ILoveDrugs)
    You've got problems? Mine's tomorrow morning.
    Likewise.
    Eeek!
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    (Original post by Fointy)
    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
    Haha, shamefully, yes!!!
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    (Original post by Fointy)
    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
    YES! I was quite disappointed :rolleyes:
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    i thought that if you differentiate y=ln3x you'd get 3/3x
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    (Original post by Fointy)
    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
    Yes - and i was going to reply with something like 'actually that took me two cosecs'... sorta had the edge taken out of it now.
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    (Original post by DominF)
    i thought that if you differentiate y=ln3x you'd get 3/3x
    Indeed, that's what I make it!
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    Isn't 3/3x the same as 1/x or should i just give up now?
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    (Original post by ILoveDrugs)
    Isn't 3/3x the same as 1/x or should i just give up now?
    Ahahaha! SO it is!
    Perhaps I should give up!
    This is why I'm applying for English at uni! Damn maths!
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    don't worry, it is :P i find the best way is to just consider that if

    y = ln f(x)

    then dy/dx = f'(x)/f(x)
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    (Original post by Fointy)
    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
    unfortunately:p:
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    (Original post by Fointy)
    Did anyone else read the title and expect this topic to involve some hilariously bad pun?
    "This is the problem: differentiate 2/cosx"

 
 
 
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