Answer: Midline equation: y = -7
Explanation: This function is a sinusoidal function of the form:
y = a.cos(b(x+c))+d
Midline is a horizontal line where the function oscillates above and below.
In the sinusoidal function d represents its vertical shift. Midline is not influenced by any other value except vertical shift. For that reason,
Midline, for the function:
is y=d, i.e.,
![y=-7](https://img.qammunity.org/2021/formulas/mathematics/middle-school/tsgnv2fisu09q2klt87m2bf6vei41e4uil.png)