Step: 1
y = 2 cos 3(
x +
π3) + 5
[Original function.]
Step: 2
It is clear that the centerline is 5 and amplitude is 2, this eliminates Graph 2.
[Since the centerline of Graph 2 is 6.]
Step: 3
From the argument (x + π3), the graph attains highest point at - π3.
Step: 4
The phase angle of the cosine function 2 cos 3(x + π3) + 5 equals the angle nearest the origin where the curve reaches the highest point above the centerline. This eliminates Graph 1.
Step: 5
The curve reaches the highest point at every half period. The period of this function is 2π3 and its half period is π3. This eliminates Graph 3.
Step: 6
As the half period of the function is - π3, label the other points left and right of - π3
Step: 7
Indicate the location of the y - axis between - π3 and π3 to complete the graph.
Step: 8
Among the given graphs, Graph 4 represents the function
y = 2 cos 3(
x +
π3) + 5.
Correct Answer is : Graph 4