For a sequence of independent Bernoulli trials each of which has success probability p, let represent the number of trials until the first success occurs and let represent the number of trials between the first and second success. Construct the joint p.m.f. on the vector . Solution assume x1 and x2 are independent p(i, j) = p1(i)p2(j) = (1 ? p)^i+jp^20 ? i, j.