What is the joint pdf of two random variables x and y?
a. f(x; y) = cx2y for 0 y x 1 and zero otherwise
b. f(x; y) = cx2y for 0 ≤ y ≤ x ≤ 1 and zero otherwise
c. f(x; y) = cx2y for 0 < x < 1 and zero otherwise
d. f(x; y) = cx2y for 0 ≤ x ≤ 1 and zero otherwise