Rederive the result shown in class, that the minimum
uncertainty 
in the position of a particle at time t
grows as
Verify explicitly that this result holds exactly in the
case of the wave packet in problem 2.4 (problem 4 of PS # 2) if we
define 
as the distance from the center of the packet
(
) to the point where the envelop decays to
of its original value.