Chapter 5, Problem 34P

Two sound waves of slightly different frequencies f₁and f₂:

$\begin{array}{l}{y}_1=\cos (2\pi f_{1}t)\\ y_2=\cos (2\pi f_{2}t)\end{array}$

produce sound that is alternating loud and soft. This phenomenon, which is called beating, is described by the equation:

$y=2\cos \left(2\pi \frac{f_1+f_2}{2}t\right)\cos \left(2\pi \frac{f_1-f_2}{2}t\right)$

Make a plot of the beating sound (shown) for $0\le t\le 0.3$ s for the case that f₁=130Hz and f₂=120Hz.