Show that the results of the preceding problem can also be obtained directly from the Langevin equation (1) of Problem 15.4 by integrating the latter over the small time interval $r$ so as to relate the velocity $\boldsymbol{t}_{\wedge}$ at time kr to the velocity $v_{k-1}$ at the time $(k-1)$ r. 8uccessive applicstion of this result then allows one to relats $v_N$ to $v_2$.