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Thread: try this...tricky

  1. Aug 31st, 2002, 11:08 PM #1
    MrPolite
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    try this...tricky

    try finding out the derivitive of this without using a calculator and then see if you got it right... for the people in highschool, you might get it wrong, believe it or not :

    y= ln(-x)









































    answer:
    1/x and not -1/x

    I know this is obvious for some people..dont say this is a stupid problem, because some people including me DO get this wrong the first time
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  2. Sep 1st, 2002, 08:03 AM #2
    DavidHooper
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    Hmm, it's good that.

    Quite funny to see people's reaction when differentiating the following, if they're not familiar with manipulating logs:
    y=ln(x)
    y=ln(x^2)
    y=ln(x^3)
    There are 10 types of people in the world - those that understand binary, and those that don't.
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  3. Sep 1st, 2002, 08:13 AM #3
    bugzpodder
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    i don't see how hard it is if you know the chain rule: y=ln(-x)
    y'=d (ln(-x))/d (-x)*d(-x)/dx
    y'=1/(-x)*(-1)
    y'=1/x
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  4. Sep 1st, 2002, 08:14 AM #4
    DavidHooper
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    I know this is obvious for some people..dont say this is a stupid problem, because some people including me DO get this wrong the first time
    There are 10 types of people in the world - those that understand binary, and those that don't.
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  6. Sep 1st, 2002, 09:45 AM #5
    marnitzg
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    Yeah its a common mistake amoung those just learning to differentiate. A lot of people also struggle with ln(1/x). But you generally learn all the tricks quite quickly
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  7. Sep 1st, 2002, 01:51 PM #6
    MrPolite
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