Cosine waves are functions of the form $x \mapsto A \cos (v x+\phi)$ where $A$ is the amplitude of the wave, $v$ the frequency, and $\phi$ the phase shift. The physical superposition of two waves is obtained mathematically by adding the two wave functions. Concern the superposition of cosine waves. The identities from Exercises 49 and 50 are particularly useful in this context.
For $\phi=0, \pi / 3,2 \pi / 3,$ and $3 \pi / 2,$ graph the superposition $x \mapsto \cos (2 x)+\cos (2 x+\phi), 0 \leq x \leq 2 \pi .$ Each of these four
curves is the graph of a wave of the form $x \mapsto A \cdot \cos$ $(2 x+\theta)$ for some amplitude $A$ and phase shift $\theta,$ each depending on $\phi .$ Use your graph to determine $A$ and $\theta$ when $\phi=2 \pi / 3 .$ Use the identity from Exercise 39 to obtain a formula for $A$ and $\theta .$ Calculate the magnitude of the superposed wave at $x=2$ for the four given values of $\phi .$ Each of these signals is less than $1.5 .$ For what value of $\phi$ is the magnitude of the superposed wave at $x=2$ as large as it can be?