Correct answer is C.
For example 2, 4, 8, 16, 32...

Cos=(adjacent/hypotenuse)
So the answer will be cos(16/20) or cos(4/5) both will give u the same answer
I hope it helps
ANSWER

EXPLANATION
The frequency of a wave function refers to the number of times the graph repeats its cycle within the interval [0,2π]
We can observe explicitly from the graph that the frequency is half.
The period of the given function is 4π


Hence the frequency is half.
The answer is C.) 4 1/4 and 5 1/2
Answer:
2,4,6,8,12,16
Because it is 2 times 3 equals 6
2 times 1 equals 2
2 times 2 equals 4
2 times 8 equals 16
2 times 3 equals 6
2 times 4 equals 8
2 times 6 equals 12
and they are all a factor of 2