Question

HELP!! MEDAL!

Answer 1

The value of cos(x) is a maximum when x = 0.
The graph in the question has its minimum value when x = 0. Therefore the sign of the term in cos(x) in the correct equation must be negative.
Do you follow this step?

Answer 2

The amplitude is given by half the difference between the maximum and minimum values of the graph. Therefore the amplitude is given by:
\[\large amplitude=\frac{5-1}{2}=2\]
The amplitude is the coefficient of the term in cos(x). Therefore the term in cos(x) is as follows:
-2cos(x)

Answer 3

The y shift of the graph is 3 units. So we must add 3 to the term in cos(x) giving the equation:
y = 3 - 2cos(x)