題組內容

5. Let $X$ and $Y$ be two random variables with joint p.d.f. given by: (10 分) \[ f(x,y) = y \cdot e^{-x}, 0 < y \le x < \infty \]

(a) Find the marginal p.d.f.'s $ f_x $ and $ f_y $, and specify the range of the arguments involved.