k), E(X2k+) = 0, k = 0,1,.... Find the (2k)! 6. Let X be a r.v. such that E(X2k) = 5 mgf of X and also its ch.f. Then deduce the distribution of X.

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**Problem Statement:**
Let \( X \) be a random variable (r.v.) such that:
\[ E(X^{2k}) = \frac{(2k)!}{k!}, \]
\[ E(X^{2k+1}) = 0, \quad k = 0, 1, \ldots \]
Find the moment generating function (mgf) of \( X \) and also its characteristic function (chf). Then deduce the distribution of \( X \).

---

**Solution Outline:**
1. **Understand the Given Information:**
   - The even moments of \( X \): \( E(X^{2k}) = \frac{(2k)!}{k!} \)
   - The odd moments of \( X \): \( E(X^{2k+1}) = 0 \)

2. **Moment Generating Function (mgf):**
   - The mgf \( M_X(t) \) is defined as \( E(e^{tX}) \).
   - Use the given moments to express \( M_X(t) \).

3. **Characteristic Function (chf):**
   - The chf \( \varphi_X(t) \) is defined as \( E(e^{itX}) \).
   - Use the results from the mgf to find \( \varphi_X(t) \).

4. **Deduce the Distribution of \( X \):**
   - Use the explicit form of \( M_X(t) \) to identify the distribution type of \( X \).

---

Begin by noting the following:

For \( k = 0 \):
\[ E(X^0) = 1 \]

For \( k = 1 \):
\[ E(X^2) = 2! / 1! = 2 \]

For \( k = 2 \):
\[ E(X^4) = 4! / 2! = 24 / 2 = 12 \]

And so on...

By recognizing these moments correspond to those of a specific type of distribution, we further compute and identify the form of \( M_X(t) \) and \( \varphi_X(t) \). Finally, we identify that \( X \) is normally distributed with mean 0 and variance 1.
Transcribed Image Text:**Problem Statement:** Let \( X \) be a random variable (r.v.) such that: \[ E(X^{2k}) = \frac{(2k)!}{k!}, \] \[ E(X^{2k+1}) = 0, \quad k = 0, 1, \ldots \] Find the moment generating function (mgf) of \( X \) and also its characteristic function (chf). Then deduce the distribution of \( X \). --- **Solution Outline:** 1. **Understand the Given Information:** - The even moments of \( X \): \( E(X^{2k}) = \frac{(2k)!}{k!} \) - The odd moments of \( X \): \( E(X^{2k+1}) = 0 \) 2. **Moment Generating Function (mgf):** - The mgf \( M_X(t) \) is defined as \( E(e^{tX}) \). - Use the given moments to express \( M_X(t) \). 3. **Characteristic Function (chf):** - The chf \( \varphi_X(t) \) is defined as \( E(e^{itX}) \). - Use the results from the mgf to find \( \varphi_X(t) \). 4. **Deduce the Distribution of \( X \):** - Use the explicit form of \( M_X(t) \) to identify the distribution type of \( X \). --- Begin by noting the following: For \( k = 0 \): \[ E(X^0) = 1 \] For \( k = 1 \): \[ E(X^2) = 2! / 1! = 2 \] For \( k = 2 \): \[ E(X^4) = 4! / 2! = 24 / 2 = 12 \] And so on... By recognizing these moments correspond to those of a specific type of distribution, we further compute and identify the form of \( M_X(t) \) and \( \varphi_X(t) \). Finally, we identify that \( X \) is normally distributed with mean 0 and variance 1.
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