Solve each problem.
(Modeling) Insect Population Suppose an insect population density, in thousands per acre, during year $n$ can be modeled by the recursively defined sequence
$a_{1}=8$
$$
a_{n}=2.9 a_{n-1}-0.2 a_{n-1}^{2}, \quad \text { for } n>1
$$
(a) Find the population for $n=1,2,3$
(b) Graph the sequence for $n=1,2,3, \ldots, 20 .$ Use the window $[0,21]$ by $[0,14]$ Interpret the graph.