Final answer:
The midline equation for the given equation y = cos((2pi/3) x) + 2 is y = 2.
Step-by-step explanation:
The midline equation represents the horizontal line through which the graph oscillates. In the given equation, y = cos((2pi/3) x) + 2, the midline equation can be found by substituting 2 for y and solving for x:
2 = cos((2pi/3) x) + 2
0 = cos((2pi/3) x)
The cosine function reaches its maximum value at 0, so the midline equation is y = 2.