What is the Marginal PDF of X?

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SUMMARY

The marginal probability density function (pdf) of the random variable X, given the joint pdf f(x,y) = 8xy for 0 ≤ x ≤ y ≤ 1, is derived by integrating over the appropriate bounds. The correct marginal pdf f_X(x) is calculated as f_X(x) = ∫(8xy) dy from x to 1, resulting in f_X(x) = 4x(1 - x^2). The integration bounds are crucial, as they define the region where the joint pdf is positive. A graphical representation of the region 0 ≤ x ≤ y ≤ 1 aids in understanding the limits of integration.

PREREQUISITES
  • Understanding of joint probability density functions (pdf)
  • Knowledge of integration techniques in calculus
  • Familiarity with the concept of marginal distributions
  • Ability to interpret graphical representations of functions
NEXT STEPS
  • Study the derivation of marginal pdfs from joint pdfs in continuous random variables
  • Learn about graphical methods for visualizing probability distributions
  • Explore the properties of continuous random variables and their distributions
  • Investigate applications of marginal pdfs in statistical analysis and probability theory
USEFUL FOR

Students studying probability and statistics, mathematicians focusing on continuous random variables, and anyone involved in statistical modeling and analysis.

Phox
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Homework Statement



Let X and Y be random variables of the continuous type having the join p.d.f.:

f(x,y) = 8xy, 0<=x<=y<=1

Find the marginal pdf's of X. Write your answer in terms of x.

Find the marginal pdf's of X. Write your answer in terms of x.

Homework Equations





The Attempt at a Solution



f1(x) = integral(8xy)dy from 0 to 1

f2(y) = integral(8xy)dx from 0 to 1

f1(x) = 4x
f2(x) = 4y

This isn't right. what am I doing wrong?
 
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Ok, so i guess the bounds of f1(x) were supposed to be from x to 1.

And the bounds from f2(y) were supposed to be from 0 to y.

But I don't don't understand why
 
Phox said:

Homework Statement



Let X and Y be random variables of the continuous type having the join p.d.f.:

f(x,y) = 8xy, 0<=x<=y<=1

Find the marginal pdf's of X. Write your answer in terms of x.

Find the marginal pdf's of X. Write your answer in terms of x.

Homework Equations





The Attempt at a Solution



f1(x) = integral(8xy)dy from 0 to 1

f2(y) = integral(8xy)dx from 0 to 1

f1(x) = 4x
f2(x) = 4y

This isn't right. what am I doing wrong?

Before doing any calculations, draw the region f > 0 in the (x,y) plane; that is, draw the region
0 ≤ x ≤ y ≤ 1.
 
I've graphed it. I'm not sure what this tells me
 
Phox said:
I've graphed it. I'm not sure what this tells me

The marginal pdf ##f_X(x)## of X is the y-integral (with fixed x), integrated over the whole relevant y-region for that value of x. The drawing tells you what that region that would be.
 

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