a) The continuous random variables X and Y have joint p.d.f.
f(x,y) = {
2e^(-x-y), 0 < x < y < ∞
0, otherwise
i) Show that the joint moment generating function of X and Y is
M_{X,Y}(t1,t2) = 2 / [(1-t2)(2-t1-t2)]; t2 < 1, t1 + t2 < 2
ii) Let U = X + Y and let V = X – 2Y. Without finding the joint p.d.f. of U and V, show that the joint m.g.f. of U and V is
M_{U,V}(t1,t2) = 2 / [(1-t1+2t2)(2-2t1+t2)]; t1 – 2t2 < 1, 2t1 – t2 < 2
iii) Find the marginal m.g.f. of U and identify its distribution.
{See Hogg, McKean and Craig, Appendix D, Pages 665-668 for a list of common distributions and their m.g.f's, which are denoted by m(t).}
iv) Are U and V independent? Give a reason for your answer.