Method of images. 14 Let p = q = In a random walk in (0, co) with an absorbing barrier at the origin and initial position at > 0, let uz,n(x) be the probability that the nth step takes the particle to the position x >  0.

Show that un() v-z,n - Va+z,n' [Hint: Show that a difference equation corre- sponding to (4.1) and the appropriate boundary conditions are satisfied.]