Let XXX and YYY be jointly continuous with PDF f(x,y)=e−x−yf(x, y) = e^{-x-y}f(x,y)=e−x−y for x,y≥0x, y \ge 0x,y≥0. What is Cov(X,Y)Cov(X, Y)Cov(X,Y)?
000
111
−1-1−1
Undefined