The amplitude of a wave corresponds to its maximum oscillation of the wave itself.
In our problem, the equation of the wave is
![y(x,t)= (0.750cm)cos(\pi [(0.400cm-1)x+(250s-1)t])](https://tex.z-dn.net/?f=y%28x%2Ct%29%3D%20%280.750cm%29cos%28%5Cpi%20%5B%280.400cm-1%29x%2B%28250s-1%29t%5D%29)
We can see that the maximum value of y(x,t) is reached when the cosine is equal to 1. When this condition occurs,

and therefore this value corresponds to the amplitude of the wave.
Answer:

Explanation:
Velocity of wave in stretched string is given by the formula

here we know that
T = 4 N
also we know that linear mass density is given as

so we have

now the tension in the string is double
so the velocity is given as


Wavelength is the distance between 2 adjacent points in a wave
we can use the following equation to find the wavelength of a sound wave
wavelength = speed / frequency
frequency is the number of waves passing a point in 1 second
substituting the values in the equation
wavelength = 343 m/s / 686 Hz
wavelength = 0.5 m
wavelength of the wave is 0.5 m
Deci, Centi, then Nano is the correct order from largest to smallest