Answer: Choice D) y = cos(2x)
Step-by-step explanation:
Normally, cosine has a period of 2pi. This means that the curve repeats itself every 2pi units. However, this graph has a period of pi.
We can see this by noting that the distance from one peak such as x = 0 to another adjacent peak x = pi is exactly pi units across.
Since T = pi is the period, we then know that
B = (2pi)/T
B = (2pi)/(pi)
B = 2
Then recall that the general template is y = Acos(B(x-C))+D
In this case, A = 1, C = 0 and D = 0. So all of this leads to y = cos(2x)