For many time series, particularly prices in speculative markets, the random walk model has been found to give a good representation of actual data. This model is written as follows: xt = xt -1 + e t...

For many time series, particularly prices in speculative markets, the
random walk
model has been found to give a good representation of actual data. This model is written as follows:

xt
=
xt-1 + et

Show that, if this model is appropriate, forecasts of
xn+h, standing at time
n, are given by