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Problem with Statistics/probability/calculus?

  1. Nov 7, 2007 #1
    1. The problem statement, all variables and given/known data

    let X denote the vibratory stress (psi) on a wind turbine at a certain wind speed. the pdf is

    f(x;y) = (x/y^2)*(e^((-x^2)/(2y^2))

    a) i need to prove that it is a pdf.
    b)assume y=100, what is the probabilty X is at most/least 200? whats prob X les than 200

    2. Relevant equations



    3. The attempt at a solution


    so i did part a part 1...f(x;y) is greter than 0 for all values...
    but for the integral of f(x)=1, i think i need to know how to integrate that, and i have no idea how!
     
  2. jcsd
  3. Nov 7, 2007 #2

    Dick

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    Try the substitution u=x^2/(2*y^2).
     
  4. Nov 7, 2007 #3
    y is a constant tho?
     
  5. Nov 7, 2007 #4

    EnumaElish

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    I think y is constant.
     
  6. Nov 7, 2007 #5

    Dick

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    Sure. You said you were integrating dx, right? y is just a parameter.
     
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