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Which of the following wave equations describes a wave with the longest wavelength?

$y(x,0)=3.0\cos\left(\dfrac{x}{1.25}\right)$

$y(x,0)=5.0\cos\left(\dfrac{2\pi x}{3.75}\right)$

$y(x,0)=1.25\cos\left(\dfrac{\pi x}{2.14}\right)$

$y(x,0)=0.33\cos\left[\dfrac{2\pi}{3}\left(\dfrac{x}{2}\right)\right]$