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Math Help - Integrating e^(-x/45)/45

  1. #1
    Senior Member chella182's Avatar
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    Integrating e^(-x/45)/45

    Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

    \int\frac{1}{45}e^{-x/45}dx

    I originally got -e^{-x/45} as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

    Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...
    Last edited by mr fantastic; August 13th 2009 at 05:16 PM. Reason: No edit - flagging the question as having been moved from Calculus because of the subsequent question.
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  2. #2
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    Quote Originally Posted by chella182 View Post
    Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

    \int\frac{1}{45}e^{-x/45}dx

    I originally got -e^{-x/45} as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

    Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...
    Both you and Maple are correct.
    Last edited by mr fantastic; September 19th 2009 at 01:16 AM. Reason: Restored original reply
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  3. #3
    Senior Member chella182's Avatar
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    Okay, but I'm stuck on this part of the question (not sure what info you'll need for it 'cause I have no idea)

    For this location, find the annual wind wpeed maximum that is likely to be exceeded once every fifty years
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    Quote Originally Posted by chella182 View Post
    Okay, but I'm stuck on this part of the question (not sure what info you'll need for it 'cause I have no idea)

    For this location, find the annual wind speed maximum that is likely to be exceeded once every fifty years
    P(x\geq x_{max})=1-P(x\leq x_{max})=1-\left[1-\exp \left(-\frac{x_{max}}{45}\right)\right]=\exp \left(-\frac{x_{max}}{45}\right)

    The integral you gave is an indefinite one, when it comes to real problems, you need to put the boundary values in, i.e. =I(x)-I(0)
    Last edited by mr fantastic; September 19th 2009 at 01:17 AM. Reason: Restored original reply
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    Quote Originally Posted by chella182 View Post
    Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

    \int\frac{1}{45}e^{-x/45}dx

    I originally got -e^{-x/45} as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

    Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...
    You are missing the constant of integration, which you will need for this to be a CDF, since you will want the function to go to 1 as x goes to infinity.

    Or rather you actualy want:


    \int_0^x \frac{1}{45}e^{-\xi/45}d\xi=1-e^{-x/45}

    CB
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