Please solve this question.

 see proof below

Step-by-step explanation:

Use the Product to Sum Identity:  cos A · cos B = [cos (A - B) + cos (A + B)]/2

Use the Odd Function Identity: cos (-A) = - cos (A)

Proof LHS → RHS:

                          = 0

LHS = RHS  

from the figure we get,

the x axis shows   the months and,

the y-axis shows the number of satisfied customer.

each line or each cell in upward direction (y-axis) shows 500.

the appropriate scale for the y - axis is: -

a = 2000 customers

b = 4000 customers

c = 6000 customers

d = 8000 customers

e = 10000 customers

f = 12000 customers

g = 14000 customers