Write the given wave equation

The wave is $y = 2\cos 2\pi(330t - x)\,\text{m}$

Compare with the standard form

The standard equation of a progressive wave is $y = A\cos 2\pi(ft - \frac{x}{\lambda})$

where:

• $A$ is amplitude
• $f$ is frequency
• $\lambda$ is wavelength

Identify the frequency

Given: $y = 2\cos 2\pi(330t - x)$

Comparing with $y = A\cos 2\pi(ft - \frac{x}{\lambda})$

we get $f = 330\,\text{Hz}$

Check options

• A: $660\,\text{Hz}$ ❌
• B: $340\,\text{Hz}$ ❌
• C: $330\,\text{Hz}$ ✅
• D: $165\,\text{Hz}$ ❌

Final answer

The frequency of the wave is $\boxed{330\,\text{Hz}}$

Comparison with stored answer

Stored correct answer: C

Our derived answer: C

Hence, the answer agrees with the stored correct answer.