Problem 1: In the population growth problem, if
b-d > 0, the population will double its present size at time T,

Problem 2: In the examples of wave motion that we studied in the
lesson, the waves traveled at a constant velocity. Such waves are
called nondispersive due to the linear relationship between the
speed of the wave and its length. This means that they don't ever
slow down, but always maintain the same speed. In the real world, the
velocity of the waves changes as a function of the properties of the
media that it travels through, primarily due to friction. Such waves
are called---you guessed it--- dispersive waves and the form of
the wave changes over time.