If the joint PDF of (X,Y)(X, Y)(X,Y) is f(x,y)=e−(x+y)f(x, y) = e^{-(x+y)}f(x,y)=e−(x+y) for x,y≥0x, y \ge 0x,y≥0, are XXX and YYY independent?
Yes
No
Only if x=yx=yx=y
Not enough information