Given that (X,Y) have pdf f(x,y)=2 and x+y=1. How do i find E(X+Y).
how doi decide the range tt i should integrate from since it cant be from infinity to neg ininty ?
I doubt that you have posted the whole question exactly as it was originally stated.
eg. The question probably said that the support was the region bounded by $\displaystyle x \geq 0$, $\displaystyle y \geq 0$ and $\displaystyle x + y \leq 1$. In which case, you set up the appropriate double integral of f(x, y) over that region.
Have you been taught double integration at all?
may i know what is the region of integration?
initially what i did was integrate from 0 to (1-y) for xf(x,y)dx + integrate from 0 to (1-x) yf(x,y)dy ...i was trying to use marginals..but i wasnt sure what is the range that i should integrate from...
from my working above, the range that i have integrated is obviously wrong..
if i were to use your method, would the range be form 0 to (1-y) dx and then 0 to 1 dy?
thanks!