Question 1 - Probability Densities (a) A joint probability density function of random variables $X$ and $y$ is given by $$ p_{X Y} (x, y)=1(x) 1y) x e^{-x(y+1)} $$ where $1(\cdot) $ is the unit step function, $1(z)=\left\ {\begin{array}{11}0, & z