Let X and Y be two random variables, and suppose that the joint density function of these
random variables is
f (x, y) ={c(x + 3y), 0 ≤x ≤1, 0 ≤y ≤1,
0, elsewhere.
1. Determine the values of c so that f (x, y) indeed represents joint probability distribution.
2. Find the correlation between X and Y .