9. Suppose that the random variables X and Y is given by f (x, y) = 6x2 y , 0 S x S y , x+yS2. a) Show that the marginal density of X is a beta density with a = 3 and ,6 = 2 . b) Derive the marginal density of Y . (120/) = 2y4,0 S y S 1;f2(y) = 2y(2-y)3,1