Answer:
[tex]f(x) = -9.1[/tex]
Step-by-step explanation:
The midline is set on [tex]f(x) = -9.1[/tex], when the sine function is equal to zero, eliminating the effect from amplitude. The midline is a horizontal line. Hence, the equation of the midline is:
[tex]f(x) = -9.1[/tex]
