We have been given that a cosine function is a reflection of its parent function over the x-axis. The amplitude of the function is 11, the vertical shift is 9 units down, and the period of the function is
. The graph of the function does not show a phase shift. We are asked to write the equation of our function.
We know that general form a cosine function is
, where,
A = Amplitude,
= Period,
c = Horizontal shift,
d = Vertical shift.
The equation of parent cosine function is
. Since function is reflected about x-axis, so our function will be
.
Let us find the value of b.




Upon substituting our given values in general cosine function, we will get:

Therefore, our required function would be
.