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Math Help - indefinite integration

  1. #1
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    indefinite integration

    I have this indefinite integral problem.. How am I supposed to go about questions like this?

    integral of ln(x)
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  2. #2
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  3. #3
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    Quote Originally Posted by dankelly07 View Post
    I have this indefinite integral problem.. How am I supposed to go about questions like this?

    integral of ln(x)
    use integration by parts with 1 as the second function
    that is make it ln(x) *1

    try the following page for more explanation
    mixture: integral of ln(x) using integration by parts
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  4. #4
    MHF Contributor Mathstud28's Avatar
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    Quote Originally Posted by dankelly07 View Post
    I have this indefinite integral problem.. How am I supposed to go about questions like this?

    integral of ln(x)
    I always suggest to people that for problems like this if it is not apparently obvious why not try a substitution? Let \ln(x)=z\Rightarrow{x=e^z}\implies{dx=e^zdz}. Then \int\ln(x)dx\overbrace{\mapsto}^{z=\ln(x)}\int{ze^  zdz}. Now it should be apparent what method to use.
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  5. #5
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    Don't integrate - balloontegrate!

    Drawing the product rule thus...



    or thus...



    ... (in which the straight lines differentiate, downwards, with respect to x) the challenge of integration by parts is to fill out the shape usefully but starting (unlike in differentiation) in one of the lower balloons...



    As with u and v, some trial and error (or intelligent forethought, or L.I.A.T.E) may be necessary - but possibly less confusing having the picture with which to find one's way. Anyway, the right road is...



    ... in which the only problem is that the lower level is no longer equal to what we wanted to integrate. So correct that...



    ... and complete the integration ...



    Balloon Calculus: worked examples from past papers
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  6. #6
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    Thanks guys all useful posts..

    balloontegrating looks nuts, but it def helps..
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