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Which of the following wave equations describes a wave with a period of $0.75\text{ s}$ and a speed of $3.25\text{ m/s}$?

$y(x,0)=2.58\cos (3.1\cdot x)$

$y(x,0)=1.25\cos (0.75\cdot x)$

$y(x,0)=0.75\cos (3.25\cdot x)$

$y(x,0)=2.4\cos (2.58\cdot x)$