Moment Generating Function of Geometric Distribution/Formulation 2/Examples/First Moment
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Examples of Use of Moment Generating Function of Geometric Distribution/Formulation 2
Let $X \sim \Geometric p$ for some $0 < p < 1$, where $\Geometric p$ is the Geometric distribution.
- $\map X \Omega = \set {0, 1, 2, \ldots} = \N$
- $\map \Pr {X = k} = p \paren {1 - p}^k$
The first moment generating function of $X$ is given by:
- $\map { {M_X}'} t = \dfrac {p \paren {1 - p} e^t } {\paren {1 - \paren {1 - p} e^t}^2 }$
Proof
We have:
\(\ds \map { {M_X}'} t\) | \(=\) | \(\ds \map {\frac \d {\d t} } {\dfrac p {1 - \paren {1 - p} e^t} }\) | Moment Generating Function of Geometric Distribution | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {-p \paren {-\paren {1 - p} e^t } } {\paren {1 - \paren {1 - p} e^t}^2 }\) | Quotient Rule for Derivatives, Derivative of Exponential Function | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {p \paren {1 - p} e^t } {\paren {1 - \paren {1 - p} e^t}^2 }\) |
$\blacksquare$