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Tough integral out of strategies

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data

    ∫x2e-2|ax| dx


    3. The attempt at a solution

    tried to integrate by parts but I just ended up with a more difficult integral including an x3 times the e-2|ax|

    I've also tried substituting y=2ax

    to get 1/(2a)∫y2e-y dx

    but where do i go from there? and can I just ignor the absolute value?


    Can anybody recommend another strategy? How can I accommodate the absolute value?

    Thank you
     
    Last edited: Sep 11, 2008
  2. jcsd
  3. Sep 11, 2008 #2
    Well, yeah...intergrate by parts!!!! and try to reduce x^2!! that is write e^(whatever) as the u'...so that when you apply the formula, you actually differentiate x^2...thus making it 2x...then do it again...and make it 2...then you will have nothing more than an integral with e(whatever that was)...You were just applying the formula wrong...and probably writing x^2 as (1/3*x^3)' ...DONT DO THAT! =)
     
  4. Sep 11, 2008 #3
    OH YEAH! DONT IGNORE THE ABSOLUTE VALUE...cause e^(-x) is a lot different that e^(x)...do you have limits on that integral?
     
  5. Sep 11, 2008 #4

    Defennder

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    Just factor out a: [tex]|ax| = |a||x|[/tex]. Keep the absolute sign there. Integration by parts works fine. Just do it twice.
     
  6. Sep 11, 2008 #5
    Thank you!
     
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