I do not understand how to get the formula from the followin

I do not understand how to get the formula from the following graph: From the figure, determine A and D and write an equation of the form v=Acosx + D (Answer: v=1-3cosx) How did they get this (I understand to reflect the function of the x- axis but am confused on how they vertically shifted the graph up 1 and have an amplitude of 3). Please show all steps and explain 4 2TT

Solution

amplitude of the given function is

( 4 + 2) / 2 = 6 / 2 = 3

so, A = 3

the graph of cos x is reflected across x axis

there is vertical shift of 1 unit upwards

so, the function becomes

Y = - 3 cos x + 1