Thread: Problem concerning Marginal Density function

I've been stuck on an assignment question for hours and I could use a little help.

The question is this:
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Given:
f(x,y) = x + y for 0 <= x, y <= 1
0 otherwise

Find the marginal densities of X and Y.
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My understanding is that the mdf f(x) is the integral of f(x,y) for all values of y. In this case, that's the integral of f(x,y) from -infinity to 1. However when I take the definite integral it goes to infinity. The same goes for the mdf f(y).

So, if somebody could offer some guidance I would be grateful.

I think that what the problem says is that both x and y are in the interval [0,1]

Wow, aren't I embarrassed. Thanks though, I would have never realized that on my own.