Answer:
option 1 ⇒ f(x) = cos (4x)
Explanation:
The general equation of the given graph is as following
f(x) = A cos (Bx)
Where A is the amplitude
and B = 2π/period
From the graph
A = 1
period = π/2
∴ B = 2π/period = 2π/(π/2) = 4
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