Given:
There are given that the parent functions as a cosine function:
Where,
The amplitude of the function is 9.
The vertical shift is 11 units down.
Explanation:
To find the cosine function, we need to see the standard form of the cosine function:

Where,
a is the amplitude of the function,
Now,
According to the question:
The amplitude of the function is 9, which means:

The vertical shift is 11 units down, which means:

For period:

Final answer:
Hence, the cosine function is shown below;