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 7pi/12. The graph of the function does not show a phase shift. What is the equation of the cosine function described?
Fill in the blanks using values from this list: -20, -11, -9, -2, 2, 9, 11, 20, 7pi/12,12pi/7,7/24,24/7
With no phase shift, the equation is: y = a·cos(b·x) + d
since this is to be a reflection of its parent function over the x-axis, a must be negative
and a is the amplitude: a = -11
b reflects the period: b = 2·pi/period ---> b = 2·pi/(7·pi/12) = 24/7
d represents the vertical d = -9
equation: y = -11·cos( (24/7)·x ) - 9