Which of the following functions is represented by the graph below?
a. y = 3 cos (1/2)x
b. y = -3 cos (1/2)x
c. y = 2 sin (1/3)x
d. y = -2 sin (1/3)x

A. y = 3 cos (1/2) x.

Step-by-step explanation:

The y-intercept is 3  so it will contain 3 cos x (because  y = cos x passes through (0, 1).

The graph of 3 cos x has been stretched horizontally  by a factor 2 ( 3 cos x would pass through (π/2, 0) whereas the given graph passes through  (π, 0).

So the equation is 3 cos(1/2) x