$21-28=$ Damped Harmonic Motion An initial amplitude $k$ ,
damping constant $c$ , and frequency $f$ or period $p$ are given. (Recall
that frequency and period are related by the equation $f=1 / p$ .
$$
\begin{array}{l}{\text { (a) Find a function that models the damped harmonic }} \\ {\text { motion. Use a function of the form } y=k e^{-c t} \cos \omega t \text { in }} \\ {\text { Exercises } 21-24 \text { and of the form } y=k e^{-c t} \sin \omega t \text { in }} \\ {\text { Exercises } 25-28 \text { . }} \\ {\text { (b) Graph the function. }}\end{array}
$$
$$
k=7, \quad c=10, \quad p=\pi / 6
$$