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Math Help - Intergral

  1. #1
    Senior Member polymerase's Avatar
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    Intergral

    \int\frac{x\;lnx}{\sqrt{1-x^2}}\;dx

    Thx
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by polymerase View Post
    \int\frac{x\;lnx}{\sqrt{1-x^2}}\;dx

    Thx
    can't really see an elegant way to do this one. but integrating by parts should work (you will need to do several substitutions afterwards, ok, like 2, "several" makes it sound like a lot), so yeah, this will be messy.

    let \frac x{\sqrt{1 - x^2}} be the functoin you integrate, i think it is convention to call this your dv and let u (the function you differentiate) be \ln x

    i'm sure one of the best integrator nominees () can find a better way to do this
    Last edited by Jhevon; January 8th 2008 at 07:14 PM.
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  3. #3
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    Quote Originally Posted by Jhevon View Post
    can't really see an elegant way to do this one. but integrating by parts should work (you will need to do several substitutions afterwards, ok, like 2, "several" makes it sound like a lot), so yeah, this will be messy.

    let \frac x{\sqrt{1 - x^2}} be the functoin you integrate, i think it is convention to call this your dv and let u (the function you differentiate) be \ln x

    i'm sure one of the best integrator nominees () can find a better way to do this
    Yes, that would work (the technique, not the last line - although that might work too [depending on what you mean by 'better']) and it's pretty routine.

    And to solve the resulting integral the substitution w^2 = 1 - x^2 would be made, followed by a spot of partial fraction decomposition.
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mr fantastic View Post
    Yes, that would work (the technique, not the last line - although that might work too [depending on what you mean by 'better']) and it's pretty routine.

    And to solve the resulting integral the substitution w^2 = 1 - x^2 would be made, followed by a spot of partial fraction decomposition.
    ah, yes! i did it the hard way, which is why i needed more than one substitutions. i let u = 1 - x^2, u^2 = 1 - x^2 does make more sense
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