Proof of MGF of some distribution in CMP of CS1

Discussion in 'CS1' started by ykai, Sep 25, 2022.

  1. ykai

    ykai Ton up Member

    In Ch3 , I can't understand some stage of proof of mgt of some distribution.
    My CMP is 2022 version.
    If possible,please tell me which theorems or how to replace the derivations to reach these conclusions.

    1.In page 9 of CH3, I don't understand why the second row becomes the third row of M_x(t) of proof of Negative binomial(k,p).
    It seems like binomial series, but I can't understand but I don't understand what's going on between the lines.

    2.In page 9 of CH3, I can't understand what happened between the first equal sign and the second equal sign in Possion.
    I can't understand how it change from sum(inf,0):(lamda*exp(t))^x/x! to exp(-lamda)*exp(-lamda*exp(t)).
     
  2. Andrea Goude

    Andrea Goude ActEd Tutor Staff Member

    Hi Ykai
    1. The summation is replaced by the binomial expansion of (1+x)^p, with x=-qe^t and p=-k, from p2 of the Tables
    2. The summation is replaced by the exponential expansion of e^x, with x=lambda*e^t , from p2 of the Tables
    Hope this helps
    Andrea
     
    ykai likes this.
  3. ykai

    ykai Ton up Member

    Thank you very much!
     

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