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Explanation:
The given equation is in the form
y = A*cos(B(x-C))+D
where
A = -2.6
B = 5
C = 0
D = 8.4
The value of D determines the horizontal axis that passes through the center of the cosine function. The equation of this axis line is y = 8.4
This is a horizontal line in which all points have y coordinate of y = 8.4
