Answer:
y = -2.5
Explanation:
For such a problem as this, you can replace all sine or cosine functions with their midline value of 0. Then you have ...
f(x) = 0 -2.5
which simplifies to ...
f(x) = -2.5
You can leave the equation like this, or write it as ...
y = -2.5
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Perhaps you can see that the midline is the value of any constant added to a sine or cosine function.