I've got a problem with a joint probability density function question.
Given f(x, y) = e^-(x+y),
0 <= x < ∞ ,
0 <= y < ∞ ,
and 0 otherwise
I need to verify that f is a valid joint PDF.
The fact that f(x, y) >= 0 for all x, y is obvious. However I'm having trouble with...