# Math Help - Marginal pdf's

1. ## Marginal pdf's

plz help to me, actually I cant find out how to got ans.

the pdf is given as
f(x, y) = 2, if (x,y) є R
else 0

there is marginal pdf's of X and Y

= 2y

then

E(X) = integral 0 to 1, x2(1-x)dx = 1/3

now can you describe this stepwise

E(X) = mathemetical expectation

becoz I cant analyse it

2. Originally Posted by yog782004
plz help to me, actually I cant find out how to got ans.

the pdf is given as
f(x, y) = 2, if (x,y) є R
else 0

there is marginal pdf's of X and Y

= 2y

then

E(X) = integral 0 to 1, x2(1-x)dx = 1/3

now can you describe this stepwise

E(X) = mathemetical expectation

becoz I cant analyse it
If the original of this question was in English please post the exact wording.

CB

3. we need to know where f(x,y)=2
The support cannot be all of R2.
probably some triangle with x<y or y<x

4. ## Intigral

Hi Captain
Hi mathengle

Here I attach one you can find it,
actually it is example of my book and cant analyse these calculation

5. I'm not sure what you want to know.
The defintion of the mean of X is

$E(X)=\int_{-\infty}^{\infty}xf(x)dx$

You first need to find the density and the support (where it is not zero).
Then integrate.

Likewise $E(X^2)=\int_{-\infty}^{\infty}x^2f(x)dx$

6. thanks mathegle

I get somethink from your suggetion, actualy I m not sure in intrigral operation and calculation, thats y i hav this confusion.