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Math Help - solvig log equation

  1. #1
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    solving log equation

    Hello, I am trying to understand how this equation works:

    formula = Vi * e^-yx
    =
    5 * e^-1*2.5
    =
    5 * e^-3.7
    =
    0.123587

    I think there must be an error ? I dont see how they went from the second to third stage.
    Thanks for any help.
    Last edited by fran1942; April 16th 2012 at 07:15 PM.
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  2. #2
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    Re: solvig log equation

    So definitely the initial question states y = 2 and x = 5 = Vi?
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  3. #3
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    Re: solvig log equation

    I have attached an image of the problem details.

    y equals the attenuation coefficient (0.01)
    x equals the distance which is stated at 2.5km.

    I just dont understand how they ended up with 0.12358 as the final answer.

    Thanks for helping.
    Attached Thumbnails Attached Thumbnails solvig log equation-calc2.jpg  
    Last edited by fran1942; April 16th 2012 at 07:48 PM.
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  4. #4
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    Re: solvig log equation

    Okay I see what the problem is,

    In the work they have done they are using beta as y not alpha,

    -1*1.48*2.5 = -3.7 (which is what they got)

    This probably wont effect you but something you should note is that the exponential should always be unit less, so this means if x = 2.5 m, then the coefficient next to x in the exponential has to be of units m-1, the question doesn't specify the units of each coefficient, alpha or beta, which makes it a little difficult to double check that it should be alpha.

    I did a google search and it seems that the units of alpha is m-1 so maybe they just made a mistake and mixed up alpha with beta?
    Thanks from fran1942
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