Answer:
f(x) = 5 cos (5/3)x - 6.
Explanation:
The function will be of the form f(x) = AcosB + c where B is the frequency.
The period of cos x is 2π and and of this function it is 6π/5 the value of B (the frequency) is calculated as follows:
Period = 2π/ B
B = 2π / 6π/5
= 5/3.
A is the amplitude which is 5 and c is the vertical displacement which is -6.