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Indepedent Variables

  1. May 18, 2013 #1
    we have X,Y variables and we have f(m,n)=P(X=m,Y=n)=C*((1/(a*m*n+15*m+11*n+8))^2)
    for what value of a X,Y are indepedent? ( its not necessery to calculate C)

    i know that f(m,n)=f(m)*f(n) if X,Y are independent but how i am gonna use this for calculate a?
     
  2. jcsd
  3. May 18, 2013 #2

    Ray Vickson

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    Never write what you did: you are using the same symbol (f) to mean three different things in the same problem. Use three different names, such as f(m,n) = g(m) * h(n).

    Anyway, you need to find a value of 'a' that makes the denominator factor into a function of n alone times a factor of m alone.
     
  4. May 18, 2013 #3
    i will estimate (a*m*n+15*m+11*n+8)^2) ? if i will do it i find 10 terms
     
  5. May 18, 2013 #4

    tiny-tim

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    Parispart, follow the advice
     
  6. May 18, 2013 #5
    i understand that i have to find a factor of n times a factor of n but i try to think how to do it using the 'a'
     
  7. May 19, 2013 #6

    haruspex

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    When you have found a, what do you think the factors will look like, in general terms? Can you write a generic form for those factors, using some other unknown constants?
     
  8. May 19, 2013 #7

    tiny-tim

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    Hi ParisSpart! :smile:

    (just got up :zzz:)
    Hint: if it was 1/(amn + m + n + 1)2,

    how would you choose a so you could factor that? :wink:

    (and what would the factors be?)
     
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