Answer:
The frequency = 5/2π
Step-by-step explanation:
* Lets revise some facts about the trigonometry function
- If the function is f(x) = A sin (B x + C) + D
* A is the amplitude
- The amplitude is the height from highest to lowest points and
divide the answer by 2
* The period is 2π/B
- The period is the distance from one peak to the next peak
- Period and Frequency are related where frequency = 1/period
* C is the horizontal shift
- The horizontal shift is how far the function is shifted to left
(C is positive) or to right (C is negative) from the original position.
* D is the vertical shift
- The vertical shift is how far the function is shifted vertically up
(D is positive) or down (D is negative) from the original position.
* Lets solve the problem
∵ f(x) = 3 cos (5x) + 2
∵ f(x) = A sin (B x + C) + D
∴ A = 3 , B = 5 , C = 0 , D = 2
∵ The period = 2π/B
∴ The period = 2π/5
∵ The frequency = 1/period
∴ The frequency = 1/(2π/5) ⇒ multiply up and down by 5
∴ The frequency = 5/2π
: you need ti divide the number of occurrences by the number of possibilities. 
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