Math Problem Statement

if X is uniform over (0,1) , calculate E(X^n) and Var(X^n)

Solution

Given that XX is uniformly distributed over (0,1)(0, 1), we know that the probability density function (PDF) of XX is:

fX(x)=1for0<x<1f_X(x) = 1 \quad \text{for} \quad 0 < x < 1

1. Calculate E(Xn)E(X^n):

The expected value E(Xn)E(X^n) is given by the following integral:

E(Xn)=01xnfX(x)dx=01xndxE(X^n) = \int_0^1 x^n f_X(x) \, dx = \int_0^1 x^n \, dx

Evaluating this integral:

E(Xn)=01xndx=[xn+1n+1]01=1n+1E(X^n) = \int_0^1 x^n \, dx = \left[ \frac{x^{n+1}}{n+1} \right]_0^1 = \frac{1}{n+1}

So, the expected value is:

E(Xn)=1n+1E(X^n) = \frac{1}{n+1}

2. Calculate Var(Xn)\text{Var}(X^n):

The variance of XnX^n is calculated using the formula:

Var(Xn)=E(X2n)(E(Xn))2\text{Var}(X^n) = E(X^{2n}) - (E(X^n))^2

First, calculate E(X2n)E(X^{2n}):

E(X2n)=01x2ndx=[x2n+12n+1]01=12n+1E(X^{2n}) = \int_0^1 x^{2n} \, dx = \left[ \frac{x^{2n+1}}{2n+1} \right]_0^1 = \frac{1}{2n+1}

Now, using the previously calculated E(Xn)E(X^n):

Var(Xn)=12n+1(1n+1)2\text{Var}(X^n) = \frac{1}{2n+1} - \left( \frac{1}{n+1} \right)^2

Simplifying this expression:

Var(Xn)=12n+11(n+1)2\text{Var}(X^n) = \frac{1}{2n+1} - \frac{1}{(n+1)^2}

Thus, the variance is:

Var(Xn)=12n+11(n+1)2\text{Var}(X^n) = \frac{1}{2n+1} - \frac{1}{(n+1)^2}

Summary:

  • E(Xn)=1n+1E(X^n) = \frac{1}{n+1}
  • Var(Xn)=12n+11(n+1)2\text{Var}(X^n) = \frac{1}{2n+1} - \frac{1}{(n+1)^2}

Would you like further details or explanations on any part of the process?

Here are 5 related questions you might find helpful:

  1. How does the uniform distribution affect expected values?
  2. Can you generalize this method for other distributions?
  3. What is the relationship between E(Xn)E(X^n) and E(X2n)E(X^{2n}) for uniform distributions?
  4. How does the variance change as nn increases?
  5. What is the role of the PDF in calculating expected values?

Tip: When dealing with uniform distributions, the calculations often simplify because the PDF is constant over the given interval.

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Math Problem Analysis

Mathematical Concepts

Probability
Uniform Distribution
Expected Value
Variance

Formulas

E(X^n) = ∫_0^1 x^n dx = 1/(n+1)
Var(X^n) = E(X^{2n}) - (E(X^n))^2
E(X^{2n}) = 1/(2n+1)

Theorems

Expected Value Theorem
Variance Formula

Suitable Grade Level

Undergraduate